The whole "Warp 10=Infinite velocity" thing was lifted out of the TNG Tech Manual
, IMO, and was meant to be the reason why ships couldn't
go to Warp 10. Ever. At least not with the current warp scale.
IIRC, the idea was that warp engine efficiency dropped dramatically as a ship neared Warp 10, ultimately requiring infinite energy to reach it. A correlation was made that an object with infinite energy would be traveling infinitely fast and would then be occupying all points in the Universe simultaneously. I think it was supposed to be an impossibility per the TNG Tech Manual
, but easily done in VOY's "Threshold."