This sounds awesome! I think it's a good idea to have leaderboards even if games already have leaderboards, because it's cool to see what people here are doing, and who knows when those leaderbards might just disappear one day. Will we be able to click and see all of a user's records for various games in one glance?
GB and NES Tetris:
Aside from marathon, can we also have leaderboards for Game B that go according to the maximum level+height cleared (and secondarily by score)?
GB Tetris DX:
The counter is pretty easy to break at 9,999,999 in this one, so I don't know if a leaderboard makes sense unless it also goes according to fewest lines needed to max the counter. There's also Ultra and timed 40L for different levels/heights. I'd say maximum score for Ultra starting from whatever level you want, and maximum level+height cleared for 40L sorted secondarily by fastest time.
Tetris DS Wifi rating:
Yes, please. I think we can trust people not to cheat, and if not, they're just as liable to lie about scores for anything else I imagine.
Tetris DS Classic:
I assume you mean Standard Marathon? Please don't include Endless. Line Clear mode would be nice too. Are Mission/Catch/Touch Tower going to be included?
Tetris Friends Marathon:
Do we really want a leaderboard for this? The scoring is so ridiculous it's hardly even Tetris.
Tetris Party:
There are actually online leaderboards in Japanese:
http://www.tetrisparty.jp/ranking_fla.html The only modes not already on the leaderboard are balance board and beginner's tetris.
The New Tetris:
I do actually have a copy of this, so yeah, I'd probably submit a score at some point. I think the marathon keeps track of lines, where the lines you are awarded depends on the types of clears you do, so your total lines is more or less a score of some sort.
Tengen Tetris:
You haven't included this, but if there were a leaderboard for marathon score I think it should be fewest lines needed to get to 999,999. The score does actually roll over to 100,000 at a million, although I've never checked to see what happens when you get to 1.1 million or 2 million, so maybe you could actually continue to make sense of the scoring beyond a million (but then this would just turn into a pointless Endless game in that case).