Shouldn't be too hard to implement with a browser source layer in the streamers OBS setup and a webserver running a script polling the blockchain for votes. That's how it was done on dlive (and probably vimm now). All of these things are doable, it's just not as user friendly as it is on twitch yet.
We can bypass twitch's "don't broadcast elsewhere" rule by only using twitch, then embedding the twitch stream in a post and using the OBS browser overlay to show extra steem vote & transfer notifications. No need to send anything steem related via twitch API :)
Another idea could be custom Steem animations that can be triggered by a Steem upvote (although with those sometimes going into the dozens or hundreds, there might need to be a minimum value) that does a short in Twitch Steem plug.
vimm.chat :)