Do you think Planetos is going to go through a colonial period? Given its considerable stakes invested in the Westerosi economy and naval power, combined with Westeros’ comparative backwardness and disunity, I can just see Braavos intervening to protect it assets and then staying for a few centuries a la Britain in India, Egypt, the Ottoman Empire, everywhere.

Probably not. The Summer Islands are too good at naval warfare, the Basilisk Isles are too unhealthy, anyone who lands on Naath dies of the butterfly plague, Sothyros is plague-ridden jungles teeming with killer dinosaurs, and Ulthos is too far away. 

As for Westeros, Braavos doesn’t have the manpower or technological edge to conquer. Westeros can raise 400,000 soldiers, Braavos probably caps out at 30,000.