That sounds a very good idea. I suppose the PS3 equivalent is pressing the PS button and picking an 'app' from the XMB, and most times the game has to be quit to launch. Even in-game shopping isn't possible. The whole experience will definitely be smoother next-gen. MS will certainly want the same apps and experiences on your PC, console and phone, so I expect one to be able to select an app from one device and have it available on the other devices. I guess the future of XBox is no longer DirectX box, but Windows Live box.They'd all be optional of course, nothing on screen. I was thinking that you can enable "widgets" as it were and they just get preloaded into ram so they are only a button press away if you need them, and they load quick and look modern. Either way there would be nothing on screen when you play. Best way to explain it I guess would be having apps minimized in Windows. I have Skype for example loaded and ready right now, but I don't see it at all. But with one mouse click it instantly appears because it's all loaded and resident in memory.
One issue I have with comparing PC functionality and things like Skype is the insane amount of bloat going on. Very efficient systems could perform online chat/video chat with little memory requirements. XB3 can do everything XB360 with exactly the same amount of 32 MBs reserved RAM ro whatever it is, although that'd go up a bit to support a 1080p UI. But it already has cross-game chat and custom soundtracks in that 32 MB, so it'd be a travesty if next-gen hundreds of MBs get used up to power Skype and friends.
A web browser could take up a significant amount (hundreds of MB), but that'd still look workable with 1/16th system RAM reserved, and an HDD for VM. Overall, I can see whatever experience being offered will be served by a standard box of CPU+GPU components and RAM and HDD/flash. The only reason I can think of for this not to be the case is if Live! is open to apps, and there are loads written that are extremely inefficient but people expect to use them on their console. As long as MS's XB division handle all the services software, they'll do an excellent job and keep impact minimal.