You make it sound so easy
1) I'm all for it, but Google needs to put its weight behind an approach like that because otherwise people will say "I like /Data better than /data or /Mydata or /MyData". It's a bit like coding conventions: everyone wants to be different.
2) Good for techy people, not so good for "normal" users. Could make it easier with a small "file manager", but that's too much work for indie devs. Could be a nice idea for a new open source project though.
3) Great idea, could actually work if the associated account would be created automatically (like in Cut the Rope for Android with Scoreloop), but:
- The backup functionality in Android for storing data in the cloud is available for API level 8 and greater, making it of not so much use when you're targeting API level 5 or 6 and greater. Could be fixed by using something like Google Storage combined with Jets3t instead, but that would be useless for apps written in C++, like many games are.
- Cloud storage isn't free. Developers can't pay for that as it would be too expensive. If every Android user would've gotten free cloud storage from Google it could be a nice alternative, but (yeah, there's always a but) most current users don't have that.
4) If you're prepared to send your trash by plane to another country, go for it!
5) Agreed. Useful for temp data.