i doubt that it can handle that many users. I even doubt it can handle enough users to cover the cost of replacing its satellites every 5 years
The tech works, its just completely non feasible. Geosync satelites can give you global access with handful of satelites.
Trans-sea cables give you cheap and quick connection speeds.
Starlink is middle of the road solution that solves both problems are immense costs.
I can only imagine high frequency traders being able to afford it vs utilise the advantage of the latencies.
They've already optimized the hell out of their latency, to a ridiculous level.