I actually have no strong opinions about whether remote work must be allowed or not... but presumably this is going to result in more people leaving, right? Presumably he knows this, right? (Maybe he's even counting on it?).

I guess this is an interesting experiment in how much staff turnover you can have at a tech company like Twitter and still do fine.

I personally would not expect it to go well. Losing everyone who knows how things work and starting over from scratch with all new employees in as short a time period as possible, or even doing your best to approach that asymptote... that can't be a good idea, can it?