As far as add-ons, Nintendo are considering you buying the older games their add on. I just hope they don't have just new pokemon in the game like with RSE because it forces you to either buy another game and trade (if you have the ability to trade with someone else, which I don't unless it can be done online or between the GBA and DS port-how plausible is that?) or use a cheat device, which I have no interest in doing because I want to use the wifi to battle fairly (I dont consider using a pokemon caught unnaturally with a cheat device fair in human battle).
So, yeah, I don't expect they will send out add ons, unless they are in the form of new games.
As for regions, I havent read anywhere the announcement about no old regions being included, do you have a link? I did think for a while that a cool idea would be to have every region, but I don't think a DS card is really big enough.