I would also like to have such weapon. Waypoints count should not be higher then 3 or 4, but it should be heavy weapon and costly ammo. Soldiers should hold only up to 3 or 4 shots for it, like anti-tank weapons like Carl Gustav. XCOM Apocalypse had also powerful launcher at end but it had only one waypoint. Other possibilty is to implement something like Homing Missile from Worms. UFO is not an artillery game, I know - but some kind of indirect artillery fire would make game much better in later stages were enemies are really tough. Unfortunately we still have no really tough enemies (2x2 monsters and something like lobstermen?).
You know, South Korea decided to field 20 mm calibre programmable grenade launcher. On side of weapons soldiers can program how long distance rounds will travel before they will explode. With such weapons can easily kill targets behind corners or cover. Its current technology on simple small grenade launcher, heavy antitank weapons currently wont allow this, but in few years it will be possible. Also rounds with IR target recognicion. In reality they will probably be forbid because they could hit civilians, but its possible to make.