If there are vulnerabilities, those vulnerabilities will be exploited. That will reduce the currency value and the value of their 'founders reward'

Not if they cash out during "IPO." I don't like the idea of a founder/developer pool, but if they are going to have one, there should be a vesting period, such that the granted coins cannot be moved for X years after receiving them. This will keep the incentive alive, and I think Ethereum would have a lot more potential if something like this was employed.

This is exactly what Zcash did. The Zcash Founders' Reward "vests" over four years.

This is an really interesting idea, but I'm genuinely curious if you have an idea as to how it might be implemented. I'm not an expert on cryptocurrencies, but I don't know how I would encode the condition "has a vulnerability been discovered this year" into the protocol.