The problem is all the diffing and stuff. You can get half a terabyte of storage for $3/mo, so glacier support isn't necessary, but getting accurate diffing is hard (there's a reason why rdiff-backup is as large as it is, and duplicating the entire thing doesn't make much sense).
I would much prefer to write a small layer to glue EncFS and rdiff-backup together (and I started doing just that: https://github.com/skorokithakis/encrups), but I haven't managed to find an elegant solution for the directory aggregation yet.
