My wish would be to do away with the distinction between levels and groups. Make them all part of a hierarchical tree replacing the furniture list and removing the tabs. Have locking and visibility be independently settable for any branch or leaf of the tree. (Currently all items in a group inherit the root parent group's visibility and currently locking something using the base plan option is a bit unwieldy too.)

Next make rooms, walls, polylines, text labels, etc. all part of the hierarchy. When trying multiple layouts where walls/rooms change shape I have a sprawling mass of levels because I have to put all the options on individual levels because I can't hide these things in a group. This results in hiding and showing multiple levels to swap between options. When you have 6 rows of tabs that constantly move position, this becomes overwhelming.

As a bonus have the option to make visibility of the children (including child-groups!) of a group be mutually exclusive with radio buttons instead of checkmarks. This would mean I could switch between options with a single click on a radio button option.

This way I could for example have... Sorry, the icons suck, but you get the idea. Layout 1 and Layout 2 are mutually exclusive. I click on the V column of Layout 2, and it is shown and Layout 1 is automatically hidden.