Beaker should have a stable, documented API for the harness to interact with it. Proposal is here:
Some discussion has already taken place on the beaker-devel mailing list:
I previously wrote a patch series to implement most (but not all) of the currently proposed API. Estimate of 10 is to allow for updating and polishing.
Two features have been deferred in the design proposal: remote logs, and accepting JSON for POST requests.
The complete patch series implementing the current version of the proposal is here:
Beaker 0.12 has been released.