Enterprise was cancelled months before Doctor Who returned to DVD, and I can't see RTD doing anything with Trek in that first year back, so if the idea ever existed, it likely died a-borning.
It was also mentioned in an interview Davies gave to the Telegraph
about a month ago. Chances are the Enterprise
crossover would have been in the "Boomtown" slot (which was a replacement for "Pompeii," which could well have been a replacement for scenery-chewing by Eccleston and Scott Bakula).