JIRA and TRAC both have remote capabilities which is how Eclipse is able to interoperate with both directly. So by that same token, you could create a ExtJS frontend for either.
However, Trac is free, JIRA is not. And there might be confusion with their open source exception, so it is best to just avoid it and any hastles that might come from that.
As for the idea of having workarounds -- I like that. Perhaps if we have our own bug database, we can restrict bug reports to only those that have workarounds. Not being in the Core group of ExtJS, I don't see much of a point of handling one otherwise.