Per a couple of discussions on enwiki, there is some demand for MediaViewer to support wikitext in the captions that appear on MMV (e.g. ''MMV'' test rendering as "MMV test", not as "MMV test").

I'm taking a look at how this might be doable myself now, although looking into it more closely, it may require a modification to be made to core before it can be implemented in the extension (specifically, to add the ThumbnailImage object to the onImageBeforeProduceHTML hook, or to add another hook post-ThumbnailImage generation) - but if need be, I can fiddle about with that.