You think I'll be able to download/stream them on the PS4 when that comes out?
Downloading changes nothing. The lack of backwards compatibility has everything to do with the processor and nothing to do with the discs.
Supposedly Sony is working on some sort of streaming thing, but I wouldn't count on it. I'm not sold on game-streaming tech in generally, it doesn't sound like it will be there at launch, and even when it does arrive who knows what the library of supported titles will be like.
If you want to play these games then get a PS3 when the price drops (there has
to be a price drop soon, they didn't even drop it when they introduced the super slim model and now the PS4 is imminent).