I think folks might be misinterpreting this a bit -- his issue with the 10-year window isn't that it will 'prevent' shares coming back into the pool (remember, the article started out talking about how employees should be able to exercise their options regardless of their cash constraints), but that giving folks the ability to wait-and-see for years, with zero risk, before pulling the trigger isn't really fair.

Let's say you are working at a start-up, and it's going well. You leave. You exercise and spend the money for your shares in your 90 day window. Great.

Now, same thing, you have a 10-year exercise window. You don't exercise because:

1. Why spend the cash?

2. Waiting will de-risk the thing.

Now the company starts struggling. You're holding 'dead' options, the company needs to recruit and expand the pool, and you get to watch from the sidelines. You may never exercise and in the mean time the pool has been refreshed unnecessarily. That's the issue. By forcing a decision, the company has a clear picture of its options pool, and employees have to make a decision based on reasonably present information.

The cash requirement of buying options sucks and I'm not sure what to do about it (if you earned it, you should be able to get it), but I agree that a 10-year window isn't the right solution either.