Kudos to kreed99 for pointing out the potentially serious downside of extra coding effort.
I've been getting paid to write code for more than 30 years. Drag-and-drop is not simple, but it's reusable, so the effort spent to make it work might well pay good dividends in other places. And the drag-and-drop that works in inventory bags might be pretty close to what's needed in the group window - depends on how the UI is coded.
Another potential problem I see is, if the server expects group member indexes in some calls, it might be really tedious to go back and remap all those calls to use redirected indexes.
If it can be done simply in a web page via a client/server model (which it can) then it can be done far easier in a dedicated local DX/Unity UI.
Coding this is not a problem, nor would it ever be in 2018+. It's entirely a choice on the part of Visionary Realms to add it to the queue of UI related tasks, that's it.
As far as locking/unlocking, just add a cutomizable modifier key(s) to hold down while adjusting it, if you want an elegant option. Something like (again, customizable) press and hold Shift-G by default, you can re-order the group, when you're done and release Shift-G, it's locked.
