Re: Any idea when the Bitcoin Mempool will stop being so congested?
UASF, UAHF, use client which follow different protocol, etc.
Non-mining full-nodes cannot change the protocol. This can only be done by miners. You want to say that full-nodes can put forward a condition that blocks will be correct if it is possible to move coin without private key. And it will force the miners to change protocol ( shoot yourself in the foot). Fantastic scenario.
You only ask how it's possible, not how it's realistic scenario (at least from today's condition)
Obviously there's no guarantee other nodes, miner (if mining/PoW is still part of newer protocol) or bitcoin community will follow newer protocol.