Thanks for taking the time to document this
I've been looking at the libgts/libproj question. On the PPA we don't have libgts as a dependency in the control file, so I'm pretty sure it's not a mandatory build time dependency. We do have libproj-dev in the PPA control file. I don't see anything in the Win Libpacks for either of these. I'm tempted to remove the libproj-dev from the daily PPA and see what happens?