I've whipped up a couple python scripts which I think could help with developing in external editors.

DO NOT run these on your only copies of data.

They haven't been tested much and could ruin your files. Please make a new copy of your cart or project folder before running either script (and generally always use git).

I haven't tested them at all for my own picotron projects yet, but it looks like they can open and save as I hoped.

The repo is here https://github.com/Gaiko-sw/picotron-external-build and it includes a readme with instructions.

The gist is that you can use the export script to turn an existing cart into a folder of lua files and a skel.p64 with the assets. You can edit the code in the lua files externally and the p64 assets in picotron, and they get pasted back together in the build step.

I'm not really sure what other people's workflows look like, but let me know if you think this could be useful.
I'll still need to test these scripts myself, but if you're brave you can try it yourself now.