What I need is a way to return the posts in a category for authors who have a particular role. I have a solution using the SQL plugin, but the query is complicated and I'd like to find a more general solution. What I would love is something like this:

<MTEntries category="X" author_role="Expert">

I know I can setvar and get the list of authors, but the author attribute only accepts one author. It doesn't look like the booleon capabilites of the tag or category attributes can be applied to the author.

Any thoughts?
Thanks

If you have custom fields plugin, you can add an additional field and use this as a filter.

A cheaper solution would be to tag expert posts as @expert and use that to filter.

I have an idea in my head about why this isn't possible/obvious, but it's a bit unformed so I'll leave it out for now.

You might experiment trying this with the Collate plugin, if only because it keeps you away from having to deal with the actual database structure. Assuming it's still compatible(should be, but haven't tried myself), it should be able to do this for you once you work out how to tell the plugin to mash the data together.