Tesla probably has their own plans for demand reduction, so I wouldn't hold my breath for them to implement a real third-party API. I have a homebrew version that uses IFTTT to automatically switch to self-consumption mode at the beginning of OhmHours and switch to backup at the end. Unfortunately the local API doesn't allow switching to TBC, so I have to do that by hand. If I have an OhmHour that's contiguous to my peak period (which ends at 7pm), I just manually extend the schedule instead.
Can OhmConnect with Sonnen battery / powerwall?