I think that the idea in the OP is excellent, and really quite elegant. I would like EU4 to have an overhauled colonial system, and this sounds like a great way to do it. Having seen the developer diaries so far, I am doubtful that anything this innovative is in store for us, however, which is quite unfortunate. It sounds as if we're going to get the same old system as before, except that now the colonist is an envoy rather than a replenishing resource. The OP's idea would certainly be far superior to EU3's old system.