As a separate issue, I now realize that current P2Pool doesn't allow *expressing* support for SegWit, due to line 372 in
work.py, which veqtrus's changes don't touch:
version=max(self.current_work.value['version'], 0x20000000),
If anyone can confirm that fixing that is as simple as changing it to
version=max(self.current_work.value['version'], 0x20000002),
This is wrong. I changed p2pool to signal
.