The Treasury Department recently issued revised final regulations under Code Section 83. While Section 83 regulations are longer and more complex, this was a short document that focuses specifically on "substantial risk of forfeiture."
So, what do these new regulations do? They add a paragraph that explains that you cannot create substantial risk by putting something in a plan document that is not going to happen and say that it creates substantial risk. In fact, they specifically say that a forfeiture provision that is not likely to be enforced (based on all the underlying facts and circumstances) does not create substantial risk.
Generally, the litmus test that is being applied is whether receipt of the property is conditioned upon performance of future services. So, for example, if nonstatutory stock options vest only if the executive works for the company for 5 years after the grant date, then there would (my read, but not a legal opinion by any means) be substantial risk of forfeiture until the options vest.
Interestingly, this regulation has retroactive applicability relating to property transferred after January 1, 2013.