Interestingly, one of your proposed colonial sites, Oman, already followed your plan, several centuries ago. They set up thalassocracies all down the coast of East Africa, and even moved their capital to Zanzibar, out-competing the incumbent Dutch and Portuguese thalassocracies. Those cities were indeed linked by trade routes, naval (but not air) power, and a common legal and administrative framework. Consider the career of Ibn Battuta, or indeed the entire Hadramawt.

What's to stop your proposed thalassocracies being displaced in exactly the same way, by other, less capitalist, imperialists, or by violent nativist sentiment?