I personally will say now, if my car (set-up with MB Slot Motor from before) dont pass the 45 degree test, no probs - Its simple, I wont bother to race.
In other words, this is only hindering the slotcar enjoyment for me and maybe for others to come.
If Chassis is FREE in RC class, I dont see a problem to use a single brand (eg. SlotIt 21k rpm/FC-130 or FK-180) type motor for what ever chassis used & then (as "south boy doctor" said

Here's to me just trying to help keep the slot car enthusiasm alive.
Luke