It may be a transition for Checkout users, but it's a shutdown for merchants.
* Shutting down payment processing which was a pretty fundamental part of the offering
* they're requiring you to reapply to get an instant buy account
* They're killing off the APIs
It's not a transition if you lose a core feature, don't transition the accounts in any meaningful way, and have to implement a new system - at that point it's about like switching to PayPal (except you get to keep payment processing if you switch).
