How big of a team costs that much? Looks like the highest listed price is $180/person/year before it becomes "call us" pricing. Im sure that enterprise plan can get expensive, but even at $500/person/year that's at least 2000 users.

I'd hope there's lots of things higher on the list of effective cost savings before trying to migrate that many users, and integrations, and history.

Such migrations are happening and will continue to happen, but I expect most will go about as well as the one discussed in a sibling comment.