An option that's available on the Pro, but not RT, is to get one of the ACDSee products. I've been using their pro photo software for almost 10 years, and currently I'm using ACDSee Pro 5.0 on the Surface Pro, to process the huge 36MP files from the Nikon D800.
It has everything you're looking for, including RAW support, editing, management, etc. Works great on the Pro.
Downside is, it's not an app; it's a full-blown program. Plus, it's not free.
They will allow a free 30 day trial, so you could always take a look.
Good luck.