>
> A limitation on most existing micropayment channel ideas is that payments
> can only flow in one direction.
>

It's worth noting that the original protocol as designed by Satoshi did not
have this limitation. It has evolved this way because of ad-hoc DoS fixes
over time (btw I'm not saying they were the wrong thing to do, as non "ad
hoc" solutions are significantly more work). But it seems like eventually a
different approach to handling DoS attacks based on resource prioritisation
and scheduling will become needed / implemented, and at that point the
original design could be safely brought back to life.