I've been thinking about this for a long while but how do you think the new Black and White versions will effect the Pokemon Video Game Championships that take place yearly? Last year's VGC's turned out to be successful and there was actual footage of a Battle Revolution battle via Wi Fi with the DS with a Ludicolo Rain Dance team which was interesting but it seemed to be a Japanese Exclusive ordeal in terms of Battle Revolution.
Considering VGC's, Black and White will need to be backwards compatible with the older DS games however given that it would be almost impossible to transfer 5th Generation Pokemon straight onto HeartGold or SoulSilver (or even Platinum) via trade on Wi Fi since the older DS games don't have data on any Pokemon past 493 which is where the current National Pokedex ends with Arceus.
So I'm thinking Nintendo will have some kind of Pal Park feature where you can migrate Pokemon from the older games but since Black and White are being released for the DS it would seem that Wi Fi Trade is the ideal choice for being able to use your old Pokemon on the new game.
Sure you can catch 1st, 2nd, 3rd, and 4th Generation Pokemon in Black and White along with the 5th Gens but it won't be the same not being able to use Pokemon from your previous games onto Black and/or White itself.
Backwards compatibility is one of the best features the 4th Generation offered and I'd hate to see Nintendo scrap it and it also makes for interesting metagames and thousands of possibilities while saving you time to train new Pokemon as well.
It was already bad enough when the Generation III games for Gameboy Advance were released as they weren't backwards compatible with the older Gameboy versions with Blue, Red, Yellow, Gold, Silver, and Crystal. That seriously takes ALOT of data and memory for a Gameboy cartridge to store.
With a DS cartridge however it's much easier but I'm really concerned that Nintendo might pull a 3rd Gen on us and force everyone to reboot. Of course I'm interested in catching the new 5th Generation Pokemon depending on what they are or If they appeal to me and Zoroark does seem interesting though.