> Highschool physics especially needs to have 'proper units at every stage of calculation' as part of the test.

Did your highschool physics not have this? I always thought it was a universal part of all physics education. Doing things like canceling out units etc. has always been a big part of high school physics, and checking that your final answer has the units it should. (If it didn't, you made a mistake somewhere.)

The idea of building units into Excel is definitely an intriguing one, though. I'm honestly kind of surprised it's the first time I've ever heard it suggested. It does seem like a pretty useful idea.