Summary
I am the original poster (OP). I would like to thank everyone who responded. I have learnt that Lightning Network is a Level 2 protocol that can work with many blockchains. It reduces fees and transaction times at the expense of some security. It is also very early days in its development and there is no guarantee that it will work at scale as its inventors hope.

The majority view seems to be that if Lightning Network works, and it is a big 'if', then it would, to some degree make altcoins slightly less attractive for smaller transactions as suggested by the original article but if you were selling something of high value like a car you are unlikely to object to the slightly higher fee and block time of the Bitcoin network.