This could easily be read that EY was acquired. Not many people quit their job and announce they're buying a house unless there is a liquidity event in their personal timeline.
It being almost exactly 4 years in makes it seem a lot more likely that he's fully vested and is now looking at doing something new.
I personally think some mix of time-based and milestone-based vesting would make sense for founders. Basically, you get some of your equity for reaching product market fit on various metrics, some for profitability, and some for scaling. A lot of startup founders would move on after reaching one of those milestones. If the company is doing very well, but you just don't want to be in the "scaling" role, you could accept longer vesting of the remaining stock in a different capacity, maybe one where you can work on another project full-time.
