Really sorry to have left this one hanging for so long. You are right this is a breaking chance since it would drop support for some of the legacy promise forms that package supports. And looking back at the timing we had already cut the 2.x release line by the time this was opened anyway.

So, what can we do? I think the best option we could do is to check if it is anything other than a native Promise and print a deprecation warning in the 2.x branch. That would set us up to remove this package and fully drop support for anything but native promises in the 3.x line which will ship with express@6. Does that sound like a good next step to you?