We can't change the license for something after you purchase, so what you purchased still belongs to you under the license you agreed to when purchasing it.
Let me take a step back and explain what led to this... An ISP purchased the powerstore and started offering it to anyone that hosted with them for $3. With the old license, this is kind of against it, but it kind of allowed it as well. Our lawyers described it as a "grey area" that would need litigation to resolve. We don't really want that.
People were already complaining that competing with a webassist $300 solution made their $2000 price-tag look bad. Imagine now competing with every ISP offering it for free. That is the long term possibility we couldn't afford, and would destroy any value our solutions have for our customers as well.
Extensions are already per developer, so they don't have that problem. They will always be sold as a tool and not a solution, so in our minds it would never make sense to move to a per-domain version.