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I think if something important as that can come out it for sure will be integrated, and i think exchanges who will integrate it first will profit and all the users will switch. I think if the LN is available it won't be that hard for the exchanges to create ln wallet for fast storage and transactions.
Why would average exchange give a damn about LN? Trades are done off-chain, large portion of bitcoin "users" don't even own wallets (buy for fiat on exchange and keep it there), to deposit - user still has to pay miner fee to open channel (so makes no sense), withdrawal fees can be passed onto users (to discourage them for withdrawing).
I don't see any immediate incentive for exchanges to implement LN. They would likely be the last to jump on it, unless there's a massive demand from users, but average traders would hardly benefit from it, if at all (with an exception of arbitrage traders).