I think only supporting jQuery and Zepto is the right decision. The percentage of developers using Dojo and YUI is very small and that number is even smaller for those using those libraries with CanJS.
Seems like a waste of Bitovi resources to be spinning cycles maintaining support when they could be better spent on features from which the greater community will benefit.
At the end of the day I don't think anyone is choosing a JavaScript framework because it supports Dojo or YUI. And for the less than 1% that do, the other 99% will be happier.