Fucking computer ate my reply.
Short answer:
GM fiat is in the nature of the position. Rules are enacted, they do not limit. Group disagreement and consensus-building is the true source of limits, and you can't make rules to create those things, it's meta-rules. A bad GM is a bad GM, whether he's playing Synnabar or UA.
Option 1 is stupid for obvious reasons.
Option 2 is stupid because it needs to decide whether it's Option 1 or Option 3. If you're playing CODA and something broken comes up and you need to errata it, it's Option 1. If you just don't like it conceptually and want to change it, it's Option 3. Besides that, all the 3E-->3.5 problems apply. Tiny incompatibilities are more annoying than total incompatibility.
Option 3 is stupid because I'd want to write UA and you'd want to write GURPS, and Bob over here would want to write Spaceman: the Trekkening, and there's no real reason for us to come to consensus, because come on, how many adventures did we all end up posting on the site anyway? A vote for Option 3 is really a vote for Option 4.
Option 4 is stupid because of
redundancy.