3cp has been tried with standin and it was dumb. Backcaps would be absolutely devastating and it would promote gunboating paintrainers trying to backcap. If the point takes forever to cap...why not just introduce more koth maps into the rotation? Koth is an exciting game mode, and koth_ashville is infinitely more fun/interesting than cp_ashville. Why can we only have one koth map? It adds variety, has shorter games, a lot of constant action. There's no need to break 5cp map that are the staple of tf2, simply introduce more fun maps over time without being limited in scope of playstyle. Over time, the maps will weed themselves out like they have been.
I think two 20 minute halves instead of two 30 minute halves would encourage more pushes as soon as you get uber rather than trying to suicide to force the other team and kind of speed up the pace. However, as we saw in europe, time based games come down to who can play more passively and force the other person to make the mistake rather than going in and taking your win by force.