It is an interesting concept. It is hard to imagine a small company could create and compete with a company like Adobe and create their own platform. But it just might work with all of the mistakes Adobe has made, there is definitely a niche to be filled.
Even DMXZone says they will continue to create and develop Dreamweaver extensions, so I don't think this is the end to anything. They state that the concept was born from the observation that "Adobe Dreamweaver is turning more and more into a tool for hardcore coders and loosing its well-known visual abilities",
I feel like the webassist extensions compliment the hardcore coders and help the common designer cross the bridge to become more hardcore, so I wouldn't be motivated by that aspect anyway. I'll keep my eye on it though. I'd be interested to see a demo once it is available.