If you hold out on refactoring to UI Router until 1.0 is released, I'm pretty confident at this point that I can promise you a smooth upgrade path well into the future. (Come to think of it, I'm still pretty confident even if you start now on 0.2.x).
When UI Router 1.0(beta/stable) will be released?
Well, we're pretty close to an alpha release. [0]
After that, it's just a matter of users testing it and telling us what's broken, and us fixing it. A few weeks, maybe?
[0] https://twitter.com/ChrisThielen/status/638040557718126592
Component Router will be the stock router in Angular 2, it is supposed to fix most of the problems with the Angular 1 router.
I've personally held off refactoring my Angular 1 routing code to UI Router because I didn't want to do it again once Component Router is released for Angular 1.3, oops I meant 1.4, oops again I think I mean 1.5. But I am starting to reconsider.