I might be wrong, but I don't think a speciation event has actually occurred with dog breeds. The two dogs you showed almost certainly would not breed, which in the wild would eventually lead to a speciation event. However if I'm not mistaken (and I may very well be) it's possible to make a great dane chihuahua mix (and other bizarrities) through artificial insemination, however it's also cruel and their will be considerable hereditary problems.
Domestic dogs are probably on the verge of a speciation event seeing as how the genetic differences are becoming great enough that cross breeding between certain breeds is incredibly difficult, and the results can be very bad. Which is the normal course. A speciation event doesn't happen all at once, but rather the likely hood of being able to produce offspring between populations becomes less and less until it reaches zero or something so close to zero it might as well be zero.
The question is can humans continue to push them genetically. Dogs aren't bred for survival, they are bred for show or other desirable attributes which leads to alot of very unhealthy breeds. Can people or should people continue to mess with the genetics of dogs for show? But that is a whole different topic.
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