It's true that nobody knows for certain what will happen. I am skeptical of the idea that bitcoin in particular will be able to scrounge up enough fees on "L1" to keep the network secure, especially given its small throughput.

As the author mentions, the "L2" scaling solutions like LN still require security on "L1". However, to the extent that "L2" is scalable, it will not increase "L1" fees.