Re: Shall menu_bar_items and tool_bar_items look at text property keymaps?

[Richard Stallman]

    I was looking at the above functions and wondered whether it really
    makes sense for those functions to look for menu-bar and tool-bar
    bindings in the keymap and local-map properties of PT in the current
    buffer?

This could cause a substantial slowdown if it means that Emacs
has to recompute the menus based on the current value of point.
The usefulness of the feature seems marginal, which suggests it 
is better not to pay that price, better not to add that feature.