Comment by rapier1

to be honest, there was a period of time in about 2010 or 2012 where I simply wasn't maintaining it as well as I should have been. I wouldn't have upstreamed it then either. That's changed a lot since then.

As an aside - you only really need HPN-SSH on the receiving side of the bulk data to get the buffer normalization performance benefits. It turns out the bottleneck is almost entirely on the receiver and the client will send out data as quickly as you like. At least it was like that until OpenSSH 8.8. At that point changes were made where the client would crash if the send buffer exceeded 16MB. So we had to limit OpenSSH to HPN-SSH flows to a maximum of 16MB receive space. Which is annoying but that's still going to be a win for a lot of users.