I've developed a working prototype with a table mode if you want to test drive it:
As it's programmed right now, it automatically sets the column widths to width of the longest text up to the maximum table width property. After that, it proportionally narrows the widths, so they fit.
Edit: Made a few changes to streamline edge scenarios that were discovered during testing. The current version of the searchable dropdown that features a table mode has now been approved and is live on the exchange:
Searchable Dropdown v.3.00