I would think that there is every need for new dog breeds. Times change and dogs have to change with them. Most of todays dogs were new breeds at one time - bred to fill a particular need of the day. As an example lets use the Beagle which has been bred through the years to be a hunting dog - and a good one at that. Beagles are lovely dogs and can be great pets in themselves but their nature requires more time and space than most people can devote to them nowadays. By cross breeding with a more homely dog you could try to start a line that would be more in tune with the lifestyles of the modern world. It seems that after all the centuries of developing new dogs to say that we have got all we need and should stop is an untenable stance to take.