design problem/question for a desk skirt

design the skirt knowing that I want the legs to be removable. Here is what I am thinking at for the moment:

You're overthinking this.

I built such a table for myself around a year ago. The apron is a continuous frame. That isn't to say the aprons are a rectangle. They are not. At each corner, the aprons come up to the legs, but are not joined to the leg with anything. At each corner, there is a diagonal part that goes from apron to apron. A screw extends from the leg to that diagonal part. The screw has wood screw thread to go into the leg, and machine screw thread to pass through the diagonal. This is what allows the leg to be removed at your convenience.

That apron assembly is joined to the top with metal Z clips available at Rockler or similar store.

In fact, the diagonal part mention above is also available as a metal bracket that functions the same.

Take a careful look at the Rockler catalog

There is no need to mortise and tenon the legs on such large table.