Currently undo is CTRL+ZKEY; inconsistent "mental chunking" with other chords of ZKEY altering shading mode. Nothing quite like checking out your model in different shading modes only to have it suddenly disappear while holding CTRL. Or, even more obtrusively, checking out your model in different shading modes and having to constantly remember not to hit Control.

I propose changing undo to be ALT+XKEY, on the basis of relevance to "erasure". Mapping of redo in particular to SHIFT+ALT+XKEY is arbitrary in this patch.