a. The pokewalker/playcoin option is awesome. Dream radar was kind of neat. b. The street pass exchange you came up with would make it too easy so they shouldn't do that. c. Creating your own gym would be great if it automatically uploaded your gym to your 3DS friends. d. The practice house should be online. e. Checking IVs would be cool. And they should make items boost IV like they have the EV ones. f. Wynaut.
They're all cool ideas, but I'd pick the playcoin store option. It's the most likely to happen.