There was a proposed patch to add AMQP support for CEL and CDRs. It's quite a good patch, and was written by our very own David Lee. If you're interested in trying them out, the patches can still be obtained from Review Board here:
Why did they not get included?
Well... the project's policy is that all new features have tests written for them in the Asterisk Test Suite. This helps to ensure that new features don't break existing features, and that new features can be maintained for a long, long time. Unfortunately, no one got around to writing tests (which is mostly my fault), and so the patches never made it in.
If there's a lot of interest in said backends, that may help generate some motion on getting some tests written, so that these backends end up in a future release.