The OP mentioned that "most parties there take minutes to process messages". My point is really that if transactions are taking minutes to complete, that's likely to be a social/structural problem, not a technical one.

With today's technology and all the work in this space, it's not particularly technically difficult to get such times down into the seconds or milliseconds, depending on the constraints.

Yes, HFT has gone to extremes to get trade execution times down as low as microseconds. And sure, that involves technical challenges. But they're mostly sort of obvious ones - you mentioned some of the major categories - that yield to throwing engineering talent at. But I was referring to the Pareto 80% of gains here.