I'm not a business expert but in my opinion Twitter would have to offer more compelling services that people would feel inclined to sign up for. A checkmark alone will just get the people that value the checkmark and a 50% reduction in ads. When anyone can get a blue checkmark it will lose some its perceived value.

Perhaps there should be a poll to see how many find the checkmark compelling enough alone to subscribe.

And Elon said that's a lie and 90% of them are bots, so...

Wonder if that includes any users from the EU? Twitter Blue isn’t even available there

Literally impossible. They’ll get 1% at best, probably 0.1% in all likelihood.