This is rather exciting. Do you think that this method can be adapted to build the pluggable transports bundles?
Yes.
I originally started working on this so I could submit a patch to include the tor-fw-helper in the TBB.
But since the helper is only needed in the PT bundles, reworking their build process seems the more productive route.
I'll see what I can do.
This is currently done semi-manually, with a makefile that builds the pluggable transports, unzips the bundle, copies in some files, and re-zips the bundle.
https://gitweb.torproject.org/pluggable-transports/bundle.git/blob/HEAD:/Mak...
We also have instructions for setting up a build VM from scratch--which it sounds like is what Vagrant does--but I guess we would instead use whatever is the build machine for the vanilla bundle.
https://gitweb.torproject.org/pluggable-transports/bundle.git/blob/HEAD:/Mak...
It would solve a lot of problems for us to have the PT bundles built at the same place and time as the vanilla bundles.