Custom editors are great!  But often when you have a custom editor, you want to restrict data entry to only use that editor, and not free-form typing in the cell.  You can prevent free-form typing in the cell by disabling the cell, but then the custom editor button is no longer available.

Suggestion is to still show custom editor button even if cell is disabled, perhaps with an additional setting; so that you could optionally not show the custom editor if the cell is disabled, since often a disabled cell should prevent any kind of modification.