Your entire premise is that old keys/users are more trusted. It is dangerous to assume this.
Right now, we extract trust from a majority vote. I'm just saying this could be another source to extract additional trust. Yes, I haven't ironed out all of the details. Let's iron them out. (And thanks for helping with this, btw).
An attacker with much less than 50% of the computing power could outrun the legitimate chain on the simple merit that he owns (or illegitimately gain access to) an old enough key...
To deal with this, keys could be registered (see below) and this registration could have a limited lifespan, and could be expired by anyone possessing a copy (if the legitimate owner retains a backup, he could send an expiration notice to the network, despite the attacker having a copy).
It would also further reduce the pseudo-anonymity of Bitcoin by correlating all blocks owned by one person by looking at which key signed them.
No, because keys registered as trust keys would have a limited lifespan, and should be expired/replaced on an on-going basis. 50%+1 attacks would likely be hit-and-runs. We probably only need the keys' registration to last a week to improve resiliency.
And it would unfairly advantage early-adopters with old keys
Not necessarily. We could require the key to be registered as a trust key at the time of block generation
, in which case, during this feature's bootstrapping, everyone would have the default level of trust. Keys cannot be retroactively registered.
Thanks again. I hope something useful comes out of this discussion.