FAA restrictions:
But they could still get approved at that height or greater, and have with some proposals. But general rule of thumb. 50 ft +/- in some cases to the max AMSL parameter.
From a project feasibility standpoint, could Miami muster a 400m ultra luxury building and sell it? Of course. Next to NYC, Miami has the market to make a project feasible in theory.
Just look at the success over in Sunny Isles Beach. Unfortunately Miami has had bad luck with its 300m proposals. They are fine selling out and building towers over 750 ft, but 1000 ft+ seems to be the unlucky line.