It's doable. Had a plugin for it on ST1, but to be honest, it wasn't really much use.
It was cool using xpath/css to create multiple selections though.
The sublime api isn't really thread safe bar set_timeout to queue callbacks in the main thread.
The way I wrote it was a bit crap so it was a bit bumpy.
I'd planned to rewrite it using generators and set_timeout for ui thread yield points, with cancellation on buffer modifications.
But you know, something shiny or something ...
Haven't ported it to ST2 yet.