If you use /waypoint with no numbers it should place a mark at your current location. Also, if you target an NPC (or a group/raid member?), it should mark that location.
I like that /waypoint without numbers shows the usage and that it expects commas between the numbers. If /waypoint without numbers put a mark at your current location, it would just immediately go away since you've arrived at the find location. You could place a mark where you currently are with "Add Label" in the map editor. You could also first get your /loc, move a little bit, and use those numbers in /waypoint There's also already a way to mark a group member (not sure about raid) through the find window. But no, there's not a way to do the same for npcs.
I was thinking these waypoints would be visible to group/raid members ? If it's just you then it's pretty useless. If you could click a spot on the map window and have it set a waypoint at that location that would be useful.