When planning PipelineTask conversion of FGCM, we recognized a Gen3-converted testdata_jointcal repo as a useful prerequisite (presumably the same is also true for a PipelineTask conversion of jointcal).
I'm not familiar enough with the structure of that package to have a plan in mind for how to organize things (or whether to try to convert the HSC data separately and before trying to convert the DECam data - I assume we'll defer the CFHT regardless). Given that there is data from multiple instruments here it could also be an interesting test of making multi-instrument Gen3 repos, but we shouldn't let that block getting something usable for PipelineTask testing. I'm hoping John Parejko (who now knows both about this data and gen2to3) might have some thoughts on those points.
Tim Jenness, if we can get this scheduled to be done by someone more familiar with the conversion code this month, that will open up Eli Rykoff to work on the actual FGCM conversion next month. I don't think it should be a lot of work, but again, I'm less knowledgeable about this package than others.