I would love to have a collapsable/expandable list of all hidden columns on a sheet with the option to unhide them from the list. This way, if I have multiple hidden columns and I just want one or two of them, I don't have to unhide everything to get to them. This would also allow you to look for columns that might be hidden without unhiding everything and needing to re-hide it again.
I know that you can unhide one column at a time, but if I have a block of 8 hidden columns and I want the 4th one, I either unhide all 8, or manually unhide 4 one at a time. Neither is ideal.