Hi Pablo,
Let me try to be concise and short, even though your questions might elicit a long answer.
regarding #1: for our next community meeting I asked that we give an insight to where we are in the extensibility target. Optimistically, the implementation should be doable by Q2. But we invite hands-on feedback from partners who ideally can report from real experiences with the current implementation of Gardener [1]. I think the Kubernetes journey for out-of-tree cloud controllers also took longer. It is a difficult decision to make. On the one hand, you want to start with the new design, but it’s not there yet. On the other hand, you want to articulate and influence the new design, but for that you need at least an experimental in-tree implementation.
regarding #2: I think the best way is indeed an agenda item in the community meeting. Overall, I understood that you are addressing what we suggested under the “gardenlet” [2]. In essence, the central Gardener is using the seed clusters for “dumb” execution. By switching the operator into the seed, and with the cluster-api spec standardized, the central Gardener can instead just multiplex the cluster order to a system that fulfills the request. And the latter could be Gardener operator (or CaaSP).
regarding #3: machine-controller is indeed independent. It actually is the best showcase of the extensibility design we have in mind.
BR Vasu
[1] https://github.com/gardener/gardener/blob/master/docs/development/new-cloud-provider.md
[2] https://github.com/gardener/gardener/blob/master/docs/proposals/01-extensibility.md#gardenlet