He also discusses the need for a change in tax treatment by the IRS. One of the fundamental issues is how options are taxed. Should you exercise an option, you will need to pay taxes on the spread (delta of strike price and current FMV, i.e. latest 409A valuation).
In many cases, the spread is so small or nonexistent, that the tax bill is irrelevant. But, in a few cases it's so large that most people can't possibly raise the capital to cover the tax bill.
I think the fundamental issue is the definition of FMV. When there's no public market, and employees are covenanting away any rights to sell their equity on secondary markets, is there really a fair market? I would say no.