What do you mean "failed"? Segwit was activated. After lots of infighting and after a hard fork for a new chain occurred but it activated on the chain that has

What do you mean "failed"? Segwit was activated. After lots of infighting and after a hard fork for a new chain occurred but it activated on the chain that has the bigger hashrate as of today. If the Bitcoin developers would push for a POS hard fork I would expect the chain to split into a POS and POW version but which version would become the canonical Bitcoin would be up for debate.