As you can see in my git history I managed to implement most of the required bitcoin api calls.

We can now verify that certain transactions have been made (if we have the tx id) so my next step is to implement the actual escrow protocol.

Iirc that requires just three more api functions (create-, sign- and sendrawtransaction) which shouldn't be difficult and some GUI elements and buttons.
At the beginning this won't be very comfortable to use (addresses and tx ids will have to be shared and typed in manually) but we can probably automate part of that process by communicating over bitmessage or direct p2p connections. But that will take more time and I'll have to ask FellowTraveler how he'd like it to be done.