hgm wrote:He must have see a complication at large depth
Probably in the last iteration that would be normal at this depth, and this takes much more time because the PV is changing early on, maybe even at root. But so what? First, that can be anything because I can't know how the opponent made up his PV anyway, and second, whatever it is - it will be one ply closer to me when it's my turn then it was to him.
As for the feedback loop - agree, that makes sense. I guess choosing the feedback factor below 1.0 moves the pole of the system into the left half of the complex plane, a mark of stable feedback systems.
However, that's actually possible with UCI, too - subtract your pondering time from the opponent's time as told with the go ponder command, and there you go. Oh, games over network and network delay? Well either the network delay is neglectable compared to the move time, or the whole setup doesn't make much sense anyway.
Sure it would be nicer if the time data were sent along with ponderhit, too, especially because engines unaware of this simply would ignore it. No special feature negotiation necessary. The problem is that there are tons of GUIs around that don't amend. Therefore, any engine that wants to support a new way has to implement both the new and the old stuff, and the result isn't simpler, it's just more convoluted.