Hi,
Welcome to the forums 
I think this is covered by @acityinohio’s proposal which seems to have the same mechanism, but rather than milestones it is features, I think.
But I see no reason why the features cannot be broken down into milestones. It might even bolster the proposal.
See the “shielded option metric” and the “what happens in case of a violation”.
Is that the sort of thing? because milestones would certainly help in the case of a violation.
And for a bit more of an explicit example
Is this more like what you were imagining? - I have pointed out before that Ethereum has much better potential to do this on chain. I think really the ECC would have to say if this model fits their development style and requirements. (milestones can be bad in some situations and development structures.)