Something I have long wondered, is why only a fairing tool is offered for curves, bot not surfaces?
Given you could take the isoparamteric curve at a control point and ‘fair’ that curve within whatever set tolerance, wouldn’t it seem not beyond possible to fair surface - perhaps with aa similar UI to endbulge (setting region to affect etc).
there is a hidden command called Elmo, which i am not fully sure why it is not an official command, it works on curves extrusions and surfaces, seems to creates fairer geometry.
Elmo is just a pre-Rhino 1.0 internal alias for the command that later got named Rebuild.
i guess you are right, i am pretty confused today. but rebuild does create a fairer surface when i see that correct, at least rebuilding curves creates a result similar to the fair command. also why is that still stuck in Rhino then. no wonder the performance keeps dropping over the generations if all the old garbage is left inside 
I would say the difference (incase it was proposed that Rebuild is a good equivalent for a Fair Surface command) is that fair for curves uses the existing structure, and also you are given a maximum deviation for the curve fairing operation. Annoyingly, rebuildUV still doesn’t even have a maximum deviation option which still puzzles me.
that is only true for degree 3 curves, fair any curve with a different degree and it will rebuild it into millions of cps.