Based on the VST3 layout I proposed this interface once:
This would be backwards compatible and would allow to opt in to the control points inside the process block.
By default it doesn’t create any overhead, because instead of calling the default value for the whole block, you can simply get the value at sample=0.
The argument in the original thread, that people with zillions of parameters preferred a callback structure, that would only fire if a value has actually changed is IMHO a completely different setup, and if that comes up again, I think those people ought to write a new framework (rant over).