Filter by "read" and/or other other more extensive filter syntax

I'm using BibBase for a number of purposes, only one (minor) of which is to list my *own* publications.
I'd also like to use this a lot for classes I'm teaching (reading lists) as well as just general "I'm currently reading this stuff"-kinda-lists or reading lists on specific topics.

To that end, I'd appreciate a more extensive/flexible filter syntax.

One possible use might be to filter for stuff I've recently read:

filter=read:true AND filter=date-modified<(current-date)-60days

Problems:
- not sure this is feasible in a URL-syntax?
- not sure how many people like this
- not sure that "date-modified" is a general BibTeX-thing; BibDesk adds it, but not sure how many other clients do.