Since KSP 1.7 Room to Maneuver released, it's time to step up our game!
Currently, when creating a planned burn, we can't adjust when and where the planned burn would occur - it's stuck there. I propose making the entire burn draggable along the orbit line so that we can make the burn occur sooner or later, depending on where did we drag the node.
We should also be allowed to put the planned burn in the next or previous orbit (so they will occur after multiple orbits - useful for interplanetary maneuvers).
How about an advanced flight computer that can reverse-calculate burns necessary to achieve certain orbit "waypoints"?
From parking orbit at Drop, the player can set a waypoint as the periapsis at Luna. Then the flight computer computes an optimal TLI time and burn magnitude and direction.