Someone to make the Iron Horse Sunday with modern geo and suspension (like that chap that cut and shut one recently, but factory). Keep the kinematics the same as the original because they rode awesome, but add modern angles and looked sweet.
Also Alan Millyard to make me one of his bikes (complete with his front and rear suspension & internal drive train) but with a single crown fork and 150ish travel.
And bring back 1.5 head tubes please with no more press for BBs, just good old threaded ones.
And as said above, big arse pivot bearings whenever possible. (Didn’t oboe of the older SC Bullits use threaded an external Bottom bracket for it’s pivot bolt?).