This[1] article from December points to a lawsuit reported by Bloomberg allegging that Marc Andreessen helped Zuckerberg push a measure through a special committee of shareholders that would allow him to maintain "voting control of the company, even if he sells most of his stock".
From some quick digging I did in a Github repo attempting to reverse-engineer the 'audio beacons', the frequencies used by at least one startup using the technique are in the 18kHz range[1].
https://outline.com