1) Ridley's a bit obvious, I've been a Metroid lover since I first played the games. And was absolutely thrilled at the sight of him in the Melee intro/the thought of him being playable. Obviously I've dealt with the years of hardship (pre-Brawl days R.I.D.L.E.Y./WoR master race), but I still persist in dreaming of a day where the biggest concern is what color alt looks best on him. I could go on forever, but just click the 8-bit Ridley in my sig to see the fruition of our work, including arguments that I myself was up until the wee hours of the morn debunking.
2) I realize you explicitly said newcomers only, implying 'veteran' characters shouldn't be listed. However, I'd very honestly prefer a reworked/designed Mewtwo rather than a copy/paste of Melee Mewtwo (who I loved playing as, for the record). This doesn't necessarily mean I want him in his new forme (which I honestly wouldn't mind one way or the other) with a completely different moveset, but rather I hope they'll make him more true to the series, and have him as a justifiable new character. Of course I'd still hope they keep certain aspects, such as the trademarked Shadow Ball/Claw.
3) I'm not even sure when my Lil' Mac appreciation truly started, myself. I grew up watching my brothers play the all the classic games, up until Super-Punch-Out!!!, and always had a soft-spot for the series even before Mac's Assist Trophy debut and remake. Playing the remake with my brothers only solidified my desire to play as him in Smash. And I figure now's as good a time as ever to make his way onto the roster.
4) While staying true to both my personal desires, and the majority of my pre-Brawl hype, I realize Krystal is nowhere near as relevant these days as I'd like to think. That said, I still honestly believe I'd rather see her than several other newcomers. The unique moveset potential is still there, and personal bias aside (I don't label either side of the "fanbase" in the wrong, though I acknowledge that it certainly has been annoying putting up with them), I think she's still one of better suggestions from her series. Granted, I don't know how well 4 StarFox characters would work out considering much more popular series still have less, and I don't actually want neither Falco or Wolf removed for her (see MorbidAltruism's THEY'RE NOT JUST CLONES OF FOX rant here), but I'd still be just as sad if she didn't make it this time around. StarFox is probably my favorite Smash series aside from Metroid (mained Fox in/since 64), so I guess you could consider this my "wishful" character.
5) Ah where to begin. I actually ran the Kamek support thread in pre-Brawl days, if anyone can remember that far back. Shouldn't come as much of a surprise that I still support him now. I would consider him a Yoshi rep, and the only plausible one at that (he's the antagonist, anyone saying Bowser/Jr. are is just arguing semantics. AND FOR THE LOVE OF PETE BOSHI IS NOT A YOSHI REP). I've always been intrigued by the concept of a dark magic user as a playable character in a game like Smash, ever since the first game. Ganondorf actually further made me wish such a character would exist, since he himself lay torn between dark magic, swordplay, and being a hairier/heavier Captain Falcon. Kamek himself has been a significantly important part of both the Yoshi and Mario series, being Bowser's most prominent right-hand minion of choice, and serving as a caretaker for the Koopa Clan in general, and basically being the guy behind the guy/the one who makes the plot possible in the first place (we all know how fun fighting a non-giant regular Koopa as a boss is). I feel like Yoshi as a series itself needs more love, what with the series having 2-3 games in between every Smash release and the new Yoshi's Island 3DS coming out soon, it should have a roster addition to at least reflect it's becoming more prominent (and kinda seems pointless to just have 1 representative justify a whole series/unique theme/icon for a series established by/in the FIRST GAME).
Lastly, my honorable mentions were mainly because I myself can't really decide who I'd prefer (Dixie or K. Rool for DK, Lyn/Micaiah/Tharja/Anna/SOMEONE WITH MAGIC OR AT LEAST AN AXE OR SOMETHING for FE, rather than just the latest flavor of the month Awakening character or fan-favorite "semi" clones (again, I'd be okay with certain people returning if they were unique))