No offense intended, but I find this to be a somewhat odd wish, as it is impossible to define a footing in any generic sense relative to a wall so that a simple on/off would do the right thing. This is one of those DWIM ("do what I mean") things. The footing size, depth, etc depends on loads, soil load-bearing capacity and too many other things for it to be magically created.
There is a reason that we model buildings the way they are built.
If one has a wall type for which a footing is known (or is to just be approximated and refined later), then just create a complex profile that includes the footing, stem, wall and whatever. Done.
PS Also - there is no reason to be attached to the Slab Tool as the tool for building footings. Any tool can be used. Short walls are much more intelligent than slabs, for example. Fat short columns are much more intelligent (snapping, size reporting, size adjustment) for isolated footings under columns. Roofs, beams and more all have uses here.
One of the forum moderators • AC 26 USA and earlier • macOS Ventura 13.2.1, iMac Pro 10-Core, Radeon Pro Vega 64