I'm not a super expert in mobile Apps so take what I say with a pinch-of-salt, however (if I can do a shameless quote-mine):
I think people want want a thing that can run apps.
I think being able to run propriety apps for other platforms on your platform shows how awesome the current platform is, if it needs apps written for it specially then I think that ditracts from the awesomeness of the platform.
+1 but as someone that isn't a super Linux Java/C++ dev, I can only imagine the chalenges and difficulties of implementing it.
Also the owners of other platforms won't take too kindly to having their app ecosystems running on other OSs