> After more than a decade at large sw companies, I can count on one hand the number of migrations where the legacy system was ever able to be turned down.

If part of the plan wasn't to run a v1 shim on top of v2 to handle legacy users that won't migrate, v2 almost certainly doesn't meet the needs of v1 customers and it's not a question of 'migration' it's a question of ending a product and releasing a similar product.

Sometimes that's what's wanted and needed, but often it's not, and then it's a surprise that the v1 users want their needs met and it's hard to say no to paying customers, but nobody signed up to run two products forever.