- The games will have backward-compatibility with the current generation games (HeartGold/SoulSilver/Diamond/Pearl/Platinum); I imagine this to be in much the same way that G/S/C did with the very first games -- you won't be able to take any new pokemon with you when you do, but you'll be able to trade between the games, and this will be necessary in order to get certain pokemon; some pokemon from Generation IV (and I and II as found in HG/SS) will *NOT* be in this game. Wi-fi plaza compatibility will probably be the same; there will probably be two Wi-fi clubs; one that works with Gen IV and one that is Gen V exclusive (again, like the G/S/C Time Capsule); you won't be able to take Gen V pokemon into the older one.
- I don't know what sort of GTS compatibility will be found, but there will still be some. It'll probably be easy enough to work around the fact that people can put up Gen IV or older pokemon and request Gen V ones (which would possibly glitch the older games if they saw those requests, not that they could fulfill them) with a GTS server-side check to prevent a Gen IV game from accessing Gen V requests; keeping in mind the GTS only displays a few results in-game out of the many offerings they have at any time (only 3-7 out of 20+), this seems fairly easy to take into account. Incidentally, given that you can't request pokemon you haven't seen, you won't be able to import Gen V pokemon into the older games, since there will be no way to see them. I think I better understand the reasoning behind this decision now.
- Naturally, the games will have some sort of DSi enhancement. A few articles have noted that the games' ID numbers imply DSi special compatibility. Exactly what this is isn't clear. It would be interesting to see SD card compatibility for saves and pokemon storage, similar to what a number of the "Pokemon Box" console titles do, and could allow for transfer of items/pokemon like in the Stadium titles. There might be additional downloadable content for the system only availiable for DSi. Graphics or framerate might improve (the generation IV titles hold a constant 30 fps due to the 3D engine, while the older games managed 60), but I'm not sure how the two systems vary graphically. I could imagine small DLC games and such for fiddling around with individual Pokemon much like how the Pokewalker works or the Sonic Advance Tiny Chao Gardens were done. Probably nothing earth-shattering (shoot, G&S were playable on the original Game Boy too). Pokemon Sunday apparently recently showed some slightly visually enhanced battle segements. Also looks like it's taking place from less of a top-down perspective, which is interesting; the 3D space wasn't really taken advantage of the way it could have been in the Gen IV titles, I'd say. Will this be the special feature for the DSi? I'm doubtful, since Super Mario 64 DS can do that sort of thing pretty well too, and that's a normal DS title.
Note the confirmation in that link on the ability to trade between the generations. Much like Arceus and Rotom can unlock areas in HG/SS, apparently some of the legendaries in the Gen IV titles will cause things to happen in these games as well.
- We'll see a Generation III remake. Almost an inevitability, really, given that DSi users have no GBA slot to use when playing the Gen. IV titles; the dual slot mode used in, say, Pal Park, is completely worthless. Besides, we've seen remakes of Gen I and II (which have been pretty successful) already, so why not? A number of people have traded in the DS for the DSi and so don't have any way to get the Gen III pokemon on their console, and besides, Pal Park is a bit rough since it deletes the pokemon off the old games in the process. This will probably put a LOT more Generation III Pokemon into play and on the GTS. I imagine the titles will be called "Radiant Ruby" and "Shimmering Sapphire" but I'm crazy so meh.
- What will we see instead of contests/Pokeathlon? This I'm less certain about, but I'm sure there's going to be something similar. If I had to venture a guess I'd think they'll probably just add more Pokeathlon events, much like how contests returned in D/P/Pt. Most of the people who have an opinion on the minigames seem to enjoy them, so it's quite believable they'd keep using them.
One thing I did hear was confirmed was additional ability to have random battles via wi-fi. Though the Battle Frontier does have a similar feature, it's crippled down to more like the gameplay in the Stadium titles since it's only 3-on-3. I'd love to be able to battle random trainers all the time and not just a few really good ones. I'm hoping they'll keep the restrictions on legendaries, too, since seriously competing with legendaries is dumb.
IGN has two other things I completely agree with. First, quit giving us all these damn TMs and instead make them dependent on items; I hate having to have a couple HM slaves for that purpose, especially given the fact that 3 of the 8 are water moves. Surf and fly, as far as I'm concerned. Maybe cut, but shoot, why not a machete or pruning shear items? Secondly, I would love to see the early common wild pokemon not be geodude and caterpie and the bird-pokemon-of-the-day. I'd like all of them to be a bit more unique, especially if it won't be until halfway through the game that we get the Time Capsule (which, honestly, who knows, at this point :P). The game, after all, is going to be set a fair ways away from the mainland, apparently!