I can only answer on a personal and little "me" level.

What "end users" need for the fitting room is a single uv-mapped object file, + a diffuse texture, + a displacement map if the clothing requires it. That is all.

Rigging? Groups? Please save yourself the trouble and keep them.

And if the target figure "is" a completely different one?

Your clothing object will get a pass through Blender (or similar) to make the initial fit.
On average this extra 'Blender" step takes 10 minutes max.

You will give your clients more trouble by delivering a grouped but unwelded mesh.
Sorry, there is so much clothing available, I just can not make the time to start welding them up. Unwelded = Garbadge can. No exeptions.

No pun intended to any one.
Just a general remark on unwelded clothing.

Exeption. Dresses with handles. they have a muli figure problem.

No idea who ever invented this, but they should be on a trip to Mars by now. LOL. (venus if female) More LOL.  => Is Venus further away then Mars? LOL-LOL-LOL-y-bol.
Another soluton in search of a problem.
The cure?
Magnets. Magnets work everywhere, before, during, and after.
And so easy, probably too easy, to reproduce and adapt.
Ok, this takes time to do. Completely agree.

Also,  do not underestimate the capabilities of the end users.
Some are learning the new tools faster then I can type here.>

PS, I still do not understand the "3 meshes"? ? ? ?

Poser 1, 2, 3, 4, 5, 7, P8 and PPro2010, P9 and PP2012, P10 and PP2014 Game Dev
"Do not drive faster then your angel can fly"!