I have played around with the campus triangle but I found a campus diamond more effective. Once your city gets going on the coast the population can rise rather quickly now the sea is a watery grassland with a lighthouse. getting to 7 pop is never an issue so a diamond is great and getting the 2 money making ones first just helps a lot. The additional trade route England gets is great but not necessary its the +2 off continent adjacency bonus combined with a cheap harbour that is great.
Is it ever viable to create commercial hubs in cities that already have a harbor?
I play a fair amount of Catherine as well as Victoria and I tend to just use the golden triangle at river mouths while with Victoria I do not care. Just having one city like this helps and especially if you like internal trade routes as they will get +3 production from the triangle as well as you getting +10 gold (with 2 adjacent sea resources). Its often you cannot even find one place for this and in which case I do not bother, no river or sea resources only means +6. It is about using your terrain to its best advantage.
For example, no river = no need for the additional CH, any district will do as you are mainly boosting the harbour adjacency. Using a campus or Theatre in this case is just fine as long as you are not relying on +3 prod internal trade routes.
I have often in the past pumped up with an encampment and IZ to +5 production. This is quite ideal in many ways, you get the large pop eurekas and all internal cities getting +5 production is pretty strong.
With Indonesia its also tempting to have a holy site in the triangle ut regardless maximizing a harbour if you have the sea resources does allow adjacency to get stronger. The trouble is the value of an adjacency card scales with the amount your civ uses it in cities.
With the advent of R&F and the +science for CH & harbour adjacency early in the game combined with naval infrastructure (+100% adjacency to harbour) and Reyna with 1 promotion for an additional 100% for both having a CH & Harbour could be a strong early option.
The one thing to keep in mind with all of this is that gold is not worth anywhere near as much as science or culture and so you have to be weary of the values you are looking at truly being of value to your nation. I think it really works with England because the synergy is so much stronger(+1 ship movement, +2 gold off continent, extra trade route). With Indonesia I am not so convinced.