Got an S2 for Christmas, and I like it so far. I also have Lumia 830, and I find myself wanting (expecting?) some of the features from WP on the Surface:
1. Separate inboxes for all of my email accounts. The mail app on the S2 is good, but I want to see what's in each account. Also, a modern outlook app would be great.
2. Battery life indicator on the start screen.
3. Notifications in one easy pull-down location.
4. A kill button on each app when you bring up the list of running apps. (I know you can just swipe down. I'm being petty.)
I guess the point of all this that if W10 for RT devices is really just a bigger version of WP10, I'll be pretty happy with that. I like the desktop, especially for managing files, but I can live without it.