I have to be honest and say that this is good idea.
I use digital speedo on cars with road tires and FWD GTR's, but RWD GTR's has analogue speedo in my cockpit.
I used to use digital for them, but i was so uncosisted because of that. I'm trying to find way to remove speedo from those but it's imposible... and i can't off all instruments because i still need some of them
Analogue is just so unrealistic on those cars... it would be better if there is nothing, so that's why i say this is a great idea.
And for open wheelers i don't know, i don't even watch that speedo on those cars, mostly because they are too fast
+1