I think i've seen something similar in a drawing somewhere, don't know if it was you or somebody else. I have no real use for high rpms, never do wood or plastics and rarely use small end mills, which have no problem running slower, so i don't need that interchangeability. If i need to do some engraving or a pcb or something like that, i can still setup my old 3040 and spare 1hp 24k rpm spindle and do it there.

I'm glad people with more experience than me don't see much wrong in that, i'll be putting it together as soon as possible.