TL/DR... No, we do not now, nor will we ever need Segwit or Lightning.
There are 3 possible vectors for maleability problems with a transaction. Type 1 and type 2 are already accounted for, and they are 99% of the maleability problem. Type 3, there is already a workaround, and there are further more elegant fixes in process down the line.
As I recall, the system will migrate over to the merchant paying the whole transaction cost, with some exceptions. Everybody benefits, the merchants pay less than what they pay Visa or Mastercard. The transaction gets locked instantly. The customers get (largely) free transactions, and instantsend will become far more common out in the real world.