A new feature introduced in the latest 365 update will allow you to highlight a portion of a formula in the formula bar and show a pop-up with the result of evaluating the highlighted expression.

https://www.youtube.com/watch?v=E0-s58Z_RSg

Previously you could use F9 to do this evaluation but it would actually replace the expression with the resulting value, so you had to ESC or CTRL-z out of it to keep from modifying the formula.