If you agree to the new business terms, you can distribute them on the App Store, on alternative app marketplaces, or both. I think that's what "and/or" means here. You are not obliged to distribute your app through alternate app marketplaces, or through the App Store. Some developers whose apps are already on the App Store won't get around to distributing their apps on the alternative marketplaces. Other developers releasing new apps will forego the App Store entirely. Once they've accepted the new terms, the new fee structures will apply to those developers regardless of which marketplace(s) they choose.

And once you've agree to the new terms, you can't switch back.

The fact that they don't allow you to transfer your apps to another developer account unless that account has also opted in to the new business terms, is new information and interesting, but not surprising. Otherwise, it would be possible to circumvent the lock-in provisions merely by creating a new developer account and transferring your apps to it.