I think development teams have to go on pushing hardware to it's limit.
In their way to that goal, they may find the space trouble. OK, no problem. They should figure out how to split it into as many DVDs as needed and carry on.
As I read earlier in this site, it would be a possibility to split the games in 1 DVD for Story Mode and another DVD for online. With that I mean that the standart would be something like "once you start story mode, you won't have to swap the disc. Same for multiplayer. Once you start playing multiplayer, forget disc swapping".
It's sad we have reached this point this early. We all knew it would arrive sooner or later... But I feel insecure regarding how PS3 can suffer collateral damage.