"After acquiring (a very successful) company I worked for, the acquiring corporation granted me, as one of very few key employees, a number of restricted stock units with 8-year cliff vesting schedule. In other words I have to stay full 8 years before any of it is vested and there are no pro-rata provisions if I’m terminated before. That is, the company can fire me after 7.5 years of service for any reason and I would lose 100% of my grant. Is this a common practice in large corporations? Is it acceptable or even legal?" Full answer thread can be found on Quora: http://www.quora.com/Is-8-years-RSU-vesting-period-acceptable?__snids__=196841088&__nsrc__=4
I haven't personally seen a cliff vest longer than 7 years on an award at anything other than a family-owned company in more than 25 years. 8 years is a long time. If it is tied to specific warranties offered by the company at the time of the transaction it may make sense. If you are building something (let's say the Hyperloop) that will take decades this may be a reasonable period.
My concern is having no consideration at all if you are a "good leaver" (someone who terminates while still in good graces). This is very uncommon at large firms.
Without knowing the specifics it is hard to say whether this ia completely stretching the limits of reasonability, but at face value it appears so.