Hi Lars,
why not accept the forking at the moment? Imho you have already sort of a new project. If you accept the forking now (relationsip statement) you can post your progress from time to time on the developers list. Your experiences will be valueable for egw. And if you have your really succeeded writing a codebase, which offers enough functionalities to become the new egw.20 base and you have a migration path, than you can call for a vote again. Accepting this is not much more, than accepting status quo, isn’t it?
But till this time you can do your work and code it in order to show us all, that your way to code everything new has really big advantages …
I would love the idea of you creating a new application first, which could be integrated in old-egw1.x, completely using your new technology. Starting with the complete platform is really very ambitious. As soon as you have enough apps written, you could write the new platform, too (user-management, app-management, language-management, domain-managemant, backup, lost-password …) but perhaps is miss some technical point, why this is to difficult.
Frank