A map idea I had a week or two ago. It's the traditional A + b > C formula (not the weird thing I did the last time I tried something like this), but capping points in different orders actually matters.
Capping A (Bridge) first causes a train carrying missiles to go from A to B, allowing players to ride the train across the map for some surprise factor when trying to then take on B. Similarly, capping B (Hopper) first causes a different train carrying boxcars from B to A, allowing for similar surprise assaults while assisting players trying to get onto the bridge itself.
Once both A and B are capped, trains no longer spawn, some doors open, spawns and spawn times change a bit, and C is ready for the taking!