My suggestion is that any binding that is part of the official distro should only be available on the marketplace as “alpha” (which by default will be filtered out by the marketplace integration in openHAB).
For the other two points: I think both should be regarded as additional possibilities that actually broaden the openHAB ecosystem and not put a threat on it. Not having to be open source might actually allow add-ons, which so far were not possible because of license restrictions. And some bindings might be so special that nobody is really interested in collaboration.
My hope is that if there are add-ons that are interesting for many in the community and where there are multiple volunteers that want to jointly work on the code together, these will actually be created as a PR so that they become part of the official distro.
Imho the best mitigation about the potential risks of this new “alternative” is to become again better on the speed of PR reviews & merges. As explained in another topic, I hope that the static analysis tool will soon help on that part.