Yes all the responses are valid technical and logistical challenges.

If there are a bunch of groups with millions to billions in assets financially incentived for something to exist then my bet is going to be on that thing to exist until such a time as the market forces change to eliminate that need

For a chain the amount of GPUs that can profitably mine is a function of token value and electricity price. For the ecosystem as a whole it’s the sum of all (GPU mining capable) chains. Take out the largest market cap chain (bitcoin doesn’t count, it’s ASIC only at this point), and you drastically reduce the total number of GPUs to saturate the crypto mining market.

There's always going to be the old Ethereum chain. No one can turn it off if people want to fork it.

Well, the current chain that everyone is following does still have the 'ice age' in it that come September will start making mining new blocks take exponentially longer to mine. If the miners want to continue with the POW chain, they'll have to coordinate a fork of their own to delay or remove the ice age. And that there is the rub. The ethereum miners have never been very good at coordinating amongst themselves.

Not to mention, Even if they fork, the value of the token depends on what the community believes it to be. Even if the majority of miners are in support of a hardfork, it's the majority of population who decides which chain has what worth (by simple supply/demand).

It will be another Ethereum Classic.

And asset-backed stable coins like USDC will not be redeemable from the GPU chain.

The energy consumption debates are a distraction from innovation, so many want The Merge to happen soon to get past this energy issue.

Ethereum "classic" is still around for the "code is law" diehards. I'd expect most of the people who are fine with the current ETH hard-fork chain will probably be fine with the merge.

It'd be interesting if we did end up with three live chains though, probably not sustainable.

It's quite likely that the old Ethereum chain will almost completely die off because although noone can force anyone not to fork it, the transaction fees on the new network will be a fraction of the old one, so there will be a big incentive for people to use the new chain.

I agree it's completely possible. I wanted to explore the possibility of forces that are powerfully incentivized for this not to happen