... I personally think it would be a HORRIBLE idea because this same thing happened when Halo 2 Vista came out...
all the pc players were excited halo 2 was coming to pc, around the same time Microsoft made vista. Microsoft made it vista only so people would buy vista. No one bought the game because very few people wanted to pay money to upgrade to vista then pay more money to buy the game (there's more to it but that is just the basics, like the stupid paying to play online and stuff)
So if what you guys are saying is that Nintendo will make it DSi only, so people will have to pay money to get the DSi, (lose features like Pal Park) then pay more money to buy the game. Then I say that is a horrible idea.
If Nintendo is any better than Microsoft they will learn from the marketing mistake Microsoft did and make it DS, DS Lite and DSi compatible.