Regarding core software commit access, I heard that there are 5 core devs who have it: Gavin, Jeff, Wladmir, Greg, Pieter

So how the implementation of another fork outside of the core repo remove their commit access?

In fact I think in a direction difference situation, if those 5 people could not reach agreement about what should be implemented in the current git repo. Then nothing can be done, since each of them have the permission to revoke any change committed by others. So if one of them want to have one commit which is not welcomed by the other people, fork is the only way to go. Otherwise any implementation will only stay at test net without any hope of entering the core repository

This is the biggest contradiction: If you want a decentralized libertarian style community, you must have hard fork. If you want to avoid hard fork, then you must use a communism model