I've never liked it, myself. A lot of people (most, probably) don't know what it means, because it's not particularly evocative of its meaning. Those three words are cut off, a fragment of the longer and more complete explanation. 'Taking as a given what remains to be proven' is a longer statement, but it has the virtue of being crystal clear. I don't think I would ever use 'begging the question' if I could make myself that clear instead.