Someone else has tried Creating shortcut (button) for "Make this the only selectable layer" in Python 2.6? but, as pointed out there, the answer doesn't work.
When adding "Make this the only selectable layer" to the ArcGIS 10.3 menu, using the Customize tool, it adds the button to the main screen, but it is permanently greyed out.
Doing it the old-fashioned way (Table of Contents -> Layer -> Selection -> Make this the only selectable layer) works just fine, but it is a bit slow.
Has anyone had/resolved this problem?