They can do that by including an XMB version of Home with "shortcuts" to various Home functions while at the same time it will make the access to Home continuous and faster.
It just changed to something a bit more like that in 1.3.5, but yeah it can go further.
Currently it is not. I have to choose a different application that feels separated from everything else and it takes time. Home should feel like an experience integrated with PS, not like a separate platform
For me the speed is not really the bottleneck, especially the loading of spaces is fast enough now. They just need a killer app I think to bring more people in. If I had a steady crew I was playing online with, I'd probably use Home more often right now already.