> Btw, giving a special address would increase the lock-in, IMHO. The newsletter owner would be dependent of Substacks benevolence forever.

It is possible, but at least writers would have the option of importing those addresses or not. Those who are suspicious that Substack will lock down the app more down the road can always opt to "rip the band-aid off" and not import the Substack app addresses.

Perhaps my main argument is "If Substack doesn't let writers migrate without forcing a behavioral change on their readers, then it is solid evidence that Substack doesn't actually care that much about reducing lock-in." The inverse is not necessarily true, and certainly I'd advise anyone who's already convinced of the consequent to not write on Substack :).