Well, I don't think it will bottleneck anything simply because you still have up to 5.5 gigs of really, really fast GDDR5 RAM. But yes, they seem to want a really smooth operating menu.
The odd thing about it is that the PS4 didn't have 8 gigs of RAM up until the right before the public unveil. They had only secured 4 gigs of GDDR5 by that time and the OS was also reported to be around 500 mb. The jump from 500mb to almost 3 GIGS is really crazy. How in the world did they bloat it up that much?
Again, I highly doubt 5.5gb is going to bottleneck anything at all (rumors are that BF4 runs at full 1080p 60fps) because the RAM they have is very competent for graphics. Modern GPU's will also have anywhere from 1-6 gigs of that same ram. PS4 still has a huge advantage over the Xbox even with the loss of RAM (also, xbox uses the same amount for their OS).
Just a bit unfortunate because I'd rather have them have the option of that much more memory instead of having a really complex OS.
The site you linked to claimed that Killzone 4 used 4.6 GB of memory, so it's not impossible for something to bottleneck, although I agree it's unlikely.
Would that Streaming feature of any game be a feature of the OS? Could even be that cross-game chat that the 360 has and now the PS4 is getting.
Don't quote me on this because there's a tiny, tiny chance I could be wrong, but almost certainly that's going to be handled by the OS since it works for every game. Handling developers doing that individually for their games would be hell.