[GordonS]

I've well aware of the OSS/FOSS definitions - it was exactly those that made me question your argument thst VS Code isn't open source. It plainly is, and indeed is Free As In Beer.

I don't see the problem with proprietary extensions - any open plugin mechanism will have at least some proprietary extensions (by the primary maintainer, or by third parties), including Theia's if it gains enough traction.