The porting should still work for chatmail but you might miss some messages until all your contacts know your new address. Indeed the manual step of enabling email forwarding is not possible with chatmail to the best of my knowledge, which is why I suggested here that the app automatically clones your account and continues to check for messages at the old address when the address is ported.
However, I assume that as a workaround you could manually clone your account before porting the address to catch any messages sent to your old address, but this is just a guess. Anyone know if this would work?
Maybe I’m wrong, but the way I understand AEAP, the notification (“Here’s my new address, please use it in future”) is sent from the new address, not from the old address, and it is only sent when you manually send a message for the first time from the new address. Therefore you can’t assume that all your contacts are already notified and that forwarding isn’t necessary.
However, maybe these issues will already be solved by the time the AEAP redesign is completed? Only those people currently working on the new AEAP or familiar with the redesign can say what to expect in future.