The possibility to designate populated colonies in a different way, not just granting independence and that's all, for example I would like to have the possibility to designate a colony as a protectorate or a vassal or a March or something else I do not know.
For each designation the player would lose direct control and would have different effects, for example a protectorate would not have the possibility to recruit ground forces or construct military ships, but still would be under the player influence especially for defence and military protection, a vassal on the contrary would have the possibility to realize military stuff but would pay periodic fee to the player and have some diplomatic possibilities.
There are really huge possibilities we can work on.
In theory, Steve could create a list of options which would represent the degree of military-economic-diplomatic possibilities of the new designated entity so that we would have several combination and not predefinite ones.
I imagine it is quite a lot of work, but It would add a LOT of gameplay and variety to the game.