Agreed. But to different degrees. In its current form this would be the strongest--since you can never leave if you want any of those shares.
Also, consider this. Someone who joined one month before IPO would get more from the kicker than someone who worked for years and then left 1 month before IPO.
Yep, I think that's a big problem. It shouldn't matter if you're still at the company when the redistribution happens, it should just be based on how many shares you own.
If you want to reduce the "golden handcuff" effect, then you can keep an account of each employees 'kicker shares', but continue to issue shares on an x every time period basis. This causes inflation in the currency of 'kicker shares'. If you stay on continuously, then you keep your percentage of the kicker. If you leave, then those shares you earned slowly deflate in value.
You could even recognize higher risk of earlier employees by issuing special shares which have some mechanism by which if they leave, those shares may still deflate, but at a slower rate than later ones. e.g. for every time-period distribution of shares, these shares receive some fraction of the new distribution.
Also, consider this. Someone who joined one month before IPO would get more from the kicker than someone who worked for years and then left 1 month before IPO.