I didn't even knew there is a braille support in tex4ht :) I know that it supports EmacsSpeak and JSpeech, I am not sure how relevant these are these days and I doubt that this support is complete.

I've done some Liblouis testing really long time ago:
http://tex.stackexchange.com/a/32685/2891
and it seemed that it works on my sample document, I am sure one would face many issues with real world documents. But what kind of document it expects other than unicode xhtml with mathml? I have impression that it should be supported, from my reading of the manual. What might be missing in usual tex4ht output are xml:lang attributes, it shouldn't be hard to add them with some configurations for babel. Again, I am not sure if Liblouis even support that :)