The problem it certainly going to be uplink/downlink - even with this massive constellation, you're fairly limited by the available RF spectrum. If you had a decently high subscription rate in a reasonably densely populated area, you'd probably be down to dozens of megabits per second per user at most.

This could deliver absolutely massively better internet in less populated areas like rural, shipping, etc. but I feel like people are perhaps getting the wrong idea and thinking this could supersede terrestrial networks in urban/surburban areas - in which case there will be a lot of disappointed people.