I got bitten by backward compatibility issues plumbing the arguments for the provision suite through test_that, run_suite, AFE RPC, and control files. I switched gears to the Autotest refactor while I waited for the dust to settle. It appears to be stable now since I have not heard of any issues since then.
I have lost track of all the bugs, but the main tracking bug for that is https://bugs.chromium.org/p/chromium/issues/detail?id=758427
Now that the plumbing is in place, all that remains is "just" adding a build stage that uses run_suite to run the provision suite.
The way provision suite is implemented won't work for tryjobs/pool:suites (I think). I'll have to dive again into the host scheduling code, but my instinct is that it would require rewriting the host scheduling code. The implementation is a hack that only works for jobs that own a pool of DUTs exclusively.