This would be a major improvement of tables in InDesign that would be the envy of any other program and I think it is possible for InDesign to do it.
This feature would automatically make a table go to its text box width with even spacing between each column of text.:
This is how it would be done with a new feature called something like 'Column Space':

(1) You would make sure the table is within a text box to the width you want the table to go to.
(2) You would then adjust the columns of text within the table to the widths you want them (as you normally would) but without using any cell indents to the left or right of each text column. (So the text column is exactly to the width of the longest line you have decided on in each column.)
(3) Between each column of text you would add this new feature column, which I've called 'Column Space'*, and this would put even spacing between each text column and this would space the table out to the text box width.

*This 'Column Space' would act like a word space in justified text, i.e. by adding a Column Space between each column of the table these special columns would behave like a word space – the columns of text would be spaced out evenly to the text box width (just as words are in justified text).

This would resolve the fiddly, trial and error issue of having to adjust table column widths to make the table go to the width you want it. This would automatically sort out the spacing between table columns automatically and accurately.

If, like me, you are working on a book with that might have 75 large tables within it, this would be a huge time saver.