Its interesting in the way that it could lead to a PoS version of bitcoin. If the miners betray the trust of users, and steal funds from Segwit adresses, the devs will fork it, rollback the theft, and use LN to validate blocks, since LN is dependable on Segwit. This would lead to a
PoS version of bitcoin.
On the other hand, we would have the Legacy mainchain keeping the same value of the forked one, due to being the longest chain in a PoW perspective (LN came only in 2017), which was not the case with BCH (which had less hashrate when it forked).
But Im probably wrong, since I dont know all the technicals about it.
It's simpler than that. The vast majority of nodes (and therefore users) would simply
ignore such a theft. He is talking about miners attempting to steal outputs going back to the P2SH fork in 2012, not just Segwit. This is in violation of consensus rules at the node level going back years. There are hardly any nodes left on the network that would view the miners' fork as valid. Even if we're just talking about hard forking to violate Segwit, 80% of reachable nodes already enforce Segwit at this time. So the fork would simply be ignored by the Bitcoin network.
Once miners realize no one's coming and they are wasting millions of dollars mining a worthless chain, they will return to the legacy chain. There would be temporarily slower block times on the legacy chain but that's about it.
I don't think miners would risk such an obvious blunder.