I can see two practical problems with this, and am curious about how they deal with them: - The investors will not be entitled to the same information as stockholders, which will limit their ability to properly value the shares. This, in turn, should increase their risk perception and lower the price they offer. - Even if the contract between the investor and the employee is sound, the employee could fail to deliver…
Look at how SharesPost and secondMarket have already solved the first problem. He second problem is just a special case, one risk.
They've solved it for more later-stage, pre-IPO companies. I'm not sure they've solved it for less well-understood companies which have raised Series A or B. I haven't looked deeply into this, so I'm prepared to stand corrected :)