If you simply right-click anywhere in their midst (or V/Alt+ right-click), that does essentially that. They will then need to spread out again, of course, but odds are they will do that anyway, even with a stop order, because when in flight they are often overlapping themselves partly. I don't really see why a special command is particularly needed in this case, but maybe I'm missing something. Also, the `/~ key is already in use; it takes you to the most recent flare.
Well, often the group is not all together; they might be spread out all over the place (e.g., due to being on LONE move mode) and I might want to have them stop just as they are with the fastest ships out front of the slow ships. Other times I will have a group which includes engineers that are toward the back of the formation and I want them all to stop to give the engineers time to fix things from the back before telling them to move again, etc.
I did use your proposed work-around, but it was not very satisfying as it cause the group to move to a specific location and spread out from there, rather than just stopping in place as I had hoped to be able to do.
Again, just right-clicking does something quite similar to this. I'm not sure what is really gained here, but again, maybe I am just missing something.
The idea of this is to get the whole group into a big mass in the shortest time possible so you can move in a group move to wherever you want to go. Yes, you can click somewhere and get them all to move, but you might not be (and probably aren't) going to get it optimized. Then, you could shift-click other movement orders and you would know once they got to that "centralized" point, the whole group would be tightly grouped no matter how far apart they were prior to that. (It's not a hard calculation, if that is the concern; it is trivially taught in a first semester classical dynamics class in college.)
Oh yes, one more thing I was going to suggest that was annoying with the Special Forces Captain:
Don't allow shift-clicking on multiple types of actions. Quite a few times I was giving circumnavigating movement orders to flank, but would at the end accidentally click too close to an enemy and my fancy 10 waypoints would then turn into an attack headlong order. If you still have shift held down, you should only allow clicks that are of the same type as those that are already queued up.
Single ship selection.
The \ key does basically this. It will select the first non-busy ship out of the current selection. It isn't by type or anything like that, but for your engineers example it works great. Someone else had wanted this for scouts, so that's why it was added. Doing something more complex like multiple \ hits probably isn't going to be possible, because as soon as you press it once, you only have a single ship left in the selection. With the L key that works only because it keeps subdividing (and in fact, you can get down to one ship of each type if you press it enough times).
I will have to try both of these options a bit and see what I can come up with. I, of course, will also have to figure out what "non-busy" means too.
Thanks for listening, as always!
Cheers...