Also, there is no genetic problem with any dog breed interbreeding with another, aside from problems caused by differences in size.
Bottom line is, there has been no "evolution" of dog breeds.
Existing genetic traits have merely been selected for and amplified by dog breeders.
These things take time. We haven't been dealing with dogs for very long. Give it a few thousand more dog generations. Speciation is virtually inevitable.
That's not entirely correct as evolution is simply the change in the frequency of alleles from one generation to the next. Selective breeding of dogs is a prime example of this. If your talking in terms of speciation then you are correct. No speciation has occurred.