I've found a very similar question: Should users be allowed to log in with the same password when a password change is requested but not changed?. But the key difference here is that requesting an email change can only be done when someone is logged in, whereas a password change (through the "forgot password" flow) can be done even when someone is logged out. It'd therefore be impossible to lock someone else out of their account if a login was not allowed while the new email hasn't been verified yet.
With that in mind, during the period between the email change request and the new email being verified, should log in with the old email be permitted (assuming that the email represents the username)?