Small communities or nations can also do some things that don't necessarily scale at large. An example of this would be Singapore and a few others I am sure we can create a short list of. I imagine tourism, banking, bitcoin mining are all possible industries if infrastructure is planned properly. I haven't gotten to the comprehensive list of the cost of infrastructure on the island itself but from preliminary calculations and research I believe that the dredging would likely be more expensive than the infrastructure itself. However, my idea is that everything would be circular and self sufficient in nature. Basically, near zero waste and life essential items such as water and food are mostly created or grown on the island. This would require a lot of forethought in the zoning and city planning department but it is not outside the realms of possibilities given that we can learn from previous examples of island nations.
You see, this is the problem, you take only the good parts from everything and ignore the rest.
Singapore is a 6 million poeple nation which is in the middle of all trading routes and it imports 90% of its food and 97% of its energy.
You can't have a thing that is in the middle of nowhere become both a tourist attraction and a banking center, you can't have both tourism and self-sufficiency in food on a small island (both Maldive and Seychelles import tons of it) and you will not get mining going with solar panels.
Not even going to mention the other fact, and this is coming from the black sheep of a 4 generation farmer family you won't get crops from that thing, not with a ton of potassium-rich fertilizer. Of course, it can be done, but the bill is going to be insane.
Btw, what is the cost for dredging enough soil to make a 47 sq miles island, even if we assume what, 1-2 meters deep ocean at that place?