The answer to this is thankfully easy and its a standard practice for large open source projects. The maintainer hierarchy does not belong to any organization. It is its own meritocracy based on an ever widening circle of trust.
Maintainers can be supported by foundation or by a private company. It does not really matter. There will be issues that multiple people will have opinion on and the best way to resolve them is by reasoning. The maintainers also have to over time come up with more explicit contribution guidelines and learn to enforce them. There would be weekly / monthly calls to discuss issues and design deliberations. Conferences and Events are a great way to build human to human contact and spirit of community, which can be supported by volunteers and foundation.
That brings us to our conference next month, and it would be awesome if many of you can attend. (https://erpnext.org/conf/2018) And maybe host events in your home cities.
We were fortunate to have Jordan Hubbard (co-creator of FreeBSD) to our 2015 conference and I had asked him this question. Its a fascinating talk if you have not heard it.