I don’t believe Twitch is investigating or considering supporting file://
So this pushes this back to a “feature suggestion” on the uservoice
https://twitch.uservoice.com/forums/310213-developers
But given the move to parent killed file:// “on purpose” I don’t expect it to be re-added as supported.
“Proper”/first party smartTV apps might get a “backdoor” to support it (or alternative ways to work) but homebrewed app’s won’t I imagine.