Honestly, I'd prefer not to be "in charge" (in any form) for GEF legacy.
Because I am not the best expert in the Eclipse platform ecosystem as a whole, I never participated in GEF development in the past.
I am not even an Eclipse committer yet, but I could try to become one.
I (together with DBeaver team) would be happy to propose PRs with bug fixes and improvements.
I would be happy to participate in discussions about GEF developments and, hopefully, participate in GEF3/GEF5 transition process.
However, I doubt that we can bring features of GEF5 into GEF3 (at least major features).
I think GEF3 API should remain the same for backward compatibility as there are hundreds of existing GEF3-based solutions. But it should be improved.
This is the main idea of my letter - return GEF3 to life to be able to fix bugs and provide minor UI or API improvements. We don't want to turn GEF3 into GEF5.
Another idea is that we could try to add support of SWT-based UI rednering into GEF5. This will solve conceptual problems with GEF3->GEF5 migration.
Briefly: the main thing we need now is a possibility to commit into GEF3 legacy repository and return GEF3 into release cycle.