Wouldn’t importing this list file be just as easy? In the end it does exactly what pihole -a addcustomdns does just on a larger scale.
Much like pihole -b -l is a quicker way to add sites to block pihole -a addcustomdns -l (or something) could allow for adding a whole list like this one.
Doesn’t need to be super complicated just expanding a little on what Pi-hole is already doing...
The same could be said for adding whitelists as well like was asked here.