After thinking about this, I'm honestly not against this suggestion.
Although I may be somewhat wrong, I believe Heavies revving and Snipers scoping at REDs is considered baiting due to the fact that from there, damaging or killing REDs is one mouse click away. However, you could argue that this applies to a lot of other primary weapons when aimed at a RED which aren't considered baiting when at a distance (Scout's scattergun & pistol, all classes that use a shotgun, Spy's revolver, etc).
As well, I feel this would actually be very beneficial to BLU Heavies in particular (especially ones that use the Brass Beast even though I hardly see that minigun be used), as they would not have to waste time revving their minigun, which REDs can use to start swarming them, and would especially help them with rebeller Scouts as they can use his revving time to sprint off and escape them.