I'm curious how this will play out over the long run. How do you reward later-stage employees fairly? A few early employees who leave the company will have an enormous advantage over later-stage employees who might do more meaningful work at the company.

In my personal experience, I joined a company mid-pivot. At the time, the strike price on the options was $75+. People who were leaving the company had strike prices around $1. That was a tricky problem there, because stock is hard to use to incentivize people when the upside is taken by people who aren't at the company any more.

One way to fix that is to issue lots of more shares, basically diluting the old employees out, but ultimately this is what these companies are trying NOT to do (effectively the 90-day window is a way of ensuring current employees' stock isn't diluted by old employees). The board isn't going to allow early investors to get diluted out, so after a few years, you're handing tiny amounts of stock to new employees. I guess the hope would be that you're paying market rate at that point?

It sounds like a good way to attract talent in an early-stage company, but after a couple of years, it's going to be tough to attract new employees (at least with stock).

These are just my opinions though, I'm convinced that unless the company is public or you're a first-20 employee, stock is not going to be worth much, especially considering the opportunity cost. There are other things that are worthwhile (it can be great for a career), but purely money-wise, you're probably going to be net-negative.