Sending small amount of BTC nowadays is not viable at all because of the fees. Will LN greatly help solve the current issue of high transaction fees?
Yes yes, this is the solving of transactions with small quantities without questioning the cost of shipping. I doubt if this can be applied in some wallet exchanges, because of course they need the benefits of each of its user transactions. So LN will be difficult to apply to all.
Also, why is Segwit not implemented by popular exchanges like Coinbase and some online wallets when it could help lower the transaction fees? I've read that the adoption rate of Segwit is merely 15-18% only and have already fallen low. If ever LN does come, would it be widely accepted or just the same as Segwit?
Actually the purpose of SegWit is to enlarge the blocksize so that the network can accommodate more transactions and not quickly clogged up, but the implementation of this with profit mining of each transaction will be cheaper than before. So there is a potential business conflict here. It takes time and gradually for all this improvement can be followed by all parties.