Googleshng:
You know, that's really 5 different questions, so I'll answer them as such.
Mature character designs? Since the primary characters in the series were all designed around 15 years ago and haven't changed since, I'm going to assume what you actually mean by that is visual style. In which case it still depends what you mean. If you mean make a game with dark and disturbing visuals, they've already done it a few times. Take for example, the bosses in tOoT. If you mean will there ever be a game in which Zelda wears nothing but a skimpy bikini and has the sort of chest that causes severe back pain, then I'm pretty darn sure the answer is no.
Mature story? Again, that could mean a few things. If you mean a story in which the aforementioned slutty Zelda is at some point wearing LESS than a skimpy bikini, the answer is a definate no. If you mean a serious thought provoking story that changes the way one looks at the world, that's never been present in ANY video game, because it simply isn't the right medium. There are countless other things you could mean by that, where my answers would run the full range of yes no and already be done, but to most of them the answer is probably no since the Zelda games are exploration/puzzle/action driven, not story driven.
Mature language: While there's an off chance that be this you mean an extremely large vocabulary, you probably mean profanity, which if you want to get technical is honestly pretty immature under most circumstances. In either case, snowball's chance of happening.
Mature gameplay quite frankly does not exist. A game can be easy, a game can be hard, and games aimed at extremely little kids tend to be easy, but it really isn't possible to create gameplay specifically intended for older players. As a general rule though, every year the average game just gets easier and easier, so you'll probably never see a Zelda game harder than the NES ones.
Finally, will Nintendo ever make an actual Zelda RPG? I wouldn't put it past them. There's TWO RPGs with Mario in them, and he doesn't even use a sword!

Googleshng:
I've gone out of my way to find one, and NOBODY in their right mind is planning to buy an X-Box. The reason for that being that quite frankly, there isn't a single worthwhile exclusive game for it. Both the PSX2 and the GameCube however have a number of droolworthy titles lined up. So, unless you want to gamble on the Gamecube completely blowing the PSX2 out of the water and everything being ported over to it, chances are you'll be stuck buying both. Don't say you can't afford to by the way, since even if you only have the money for one now, you can always get the other used for dirt cheap down the line. That being said, I would recommend getting the Gamecube first because there's at least half a dozen games coming out for it that I'm looking forward to before even one hits the PSX2. Of course, none of the RPGs I'm looking forward to on EITHER system have US release dates at this time, so to go by my opinion you'd have to have the same taste in action and adventure games as I do... and whatever genre Pikmin fits into. Even if you don't though, it's cheaper, a better piece of hardware, and has a WONDERFUL controller design, so odds are you'll still find some games to play on it. At this point though, if you want a new system to play RPGs on, you should just get a Gameboy Advance. It's SWARMING with upcoming RPGs. Plus it's only $100, so you can get yourself some more games with the extra cash.

Googleshng:
In no particular order: Pikmin, Resident Evil 0, WarCraft 3, Shadow Hearts, and if I'm allowed to say it, Hoshigami. There's a lot more, but those are the ones I know the most about at this time, and the more I know, the more I tend to drool.

Googleshng:
While none of these answers are concrete, right now I'll have to say... RPG: Skies of Arcadia, Moment: the scene when your party is split up in Skies of Arcadia, Hero: Myau from Phantasy Star, Heroine: Koudelka (from Koudelka but I'd think that's a given), and Villain: Kefka from FF6. Honorable mention goes to Magus for spiffiest turncoat. A surprising 50-50 split between Overwerks and people who at one point worked for Square, although had I answered the question as posed it would have been 3 to 1. You know, if I could get everyone reading this column to play the Phantasy Star series from the beginning and Skies of Arcadia, it would SERIOUSLY shut me up. 8)

Googleshng:
That, the rest of Wall Market, and the fact that you can go on a date with Barret.

Googleshng:
Now that I'd like to see a picture of. Anyway though, it's rather hard to put into words what makes Skies of Arcadia such a wonderful game. Aside from every individual aspect of the game being masterfully done (setting, character designs, game mechanics, music, etc.) it has an intangable quality to it that really makes you love every second of the game. The best way I can describe it is that every single insignificant little detail of the game gives the impression that somebody poured their heart and soul into making it just right. I wish I could put that in less poetic terms, but that's the best I can do, and everyone I know who's played the game has even more trouble putting that into words. In any case though, considering the fact that everyone I know who's played it feels the same way as I do about it, and trust me, I know some REALLY jaded people, I can say with near certainty that you won't regret getting a DC for SoA's sake. Especially considering how dirt cheap they are now.

Googleshng:
A couple of people jumped all over this one. That's the thing about simple little symbols. More than one group is going to come up with signifigance for them. Swastikas and pentagrams in particular were both stolen pre-existing symbols before being stolen by unsavory types and given their current reputations, plus groups halfway around the world use them in totally different contexts. Other examples include the spiral pattern used for the Dreamcast logo, and the traditional smiley face: =) which looks like the katakana for both shi and tsu (as some may remember from my having it wrong in my sig pic for a while).

Googleshng:
You can make Harle a permanent member of your party the same way as anyone else. Go win while you have her. Next time you play, she'll join up at the same time as everyone else you got on previous plays through the game.

Googleshng:
I avoid MMORPGs like the plague, but were I in your shoes, the first thing I would do would be to find someone who's filthy stinking rich, and strike up a deal with them. Something along the lines of, say, you being their personal servant for a nice salary. You run magic items back to town to sell for'em, spy on his enemies, and things like that, and in return, he gives you the occassional big wad of cash. Since a realistic economy is one of the things they wanted that game to have, that sort of arrangement should sit just fine with your personal ethics, and if it doesn't, just promise yourself that once you're rolling in the dough, you'll hire a servant of your own to balance things out. As for "Graphicless graphics" as you put it, assuming you're refering to the graphics engine for my game, well, hold out a while longer and I should have some screens to demonstrate it with. Just don't ask me to define "a while".

Googleshng:
Honestly speaking? I wouldn't recommend any of those games. If I were in your shoes, I would ease them in with a nice Action/RPG like Secret of Mana, then hit Paper Mario, maybe Valkyrie Profile, then dive right in to a first rate game like FF6, Skies of Arcadia, or maybe Lunar if he isn't big on graphics. Not Xenogears though. That's seriously for the hardcore RPGamer only. Out of what you have though, you should probably go with FF4. It's not as dull as Grandia, as hard as Lunar, or as atypical as Chrono Cross. Chrono Trigger would be even better, but I'm told the load times on the PSX port are rather nasty. Actually, now that I think about it, maybe Chrono Trigger WOULD be the safer bet. Better graphics, anime cut scenes wedged in, and it's a bit more action oriented. Oh, and I really should mention since I started this reply with the word honestly that I personally would never try to get someone into RPGs in the first place, but that's mostly just because I don't know anyone who doesn't play them already.