If LN - with Bitcoin - works as expected, it will be surely the "hangman" for a lot of altcoins:
- Those that promise scaling with unsustainable models (like simple big blocks - BCH, I'm looking at you
)
- Many of those that are marketing themselves as an alternative to Bitcoin because of the "high fees" there, but have nothing else to offer.
But altcoins that have interesting and sound technical proposals that solve real problems and can't simply be adopted by Bitcoin, won't get affected, I think. Also altcoins with sound and novel DAG- and "chain-based"* scaling solutions (child-chains, pegging mechanisms for sidechains etc.) would still have a chance to succeed, because off-chain transactions are, in some aspects, inferior to on-chain transactions (they can be reverted in certain circumstances).
*
"chain-based" scaling, for me, are models where the traditional transaction model - a transaction is confirmed by a validator that creates "blocks" - is preserved. It's different than "on-chain-scaling" - this word, for me, only implies models where everything occurs at the "main chain".