How cool would it be as you can asign a DNS request to another URL
So lets say someone in the network type in www.google.com and the pihole redericts to www.duckduckgo.com
That would be possible, but only in a very limited fashion.
host duckduckgo.com
duckduckgo.com has address 46.51.197.89
duckduckgo.com has address 52.50.207.201
duckduckgo.com has address 176.34.131.233
duckduckgo.com has address 176.34.155.20
duckduckgo.com has address 54.229.105.203
duckduckgo.com has address 54.229.105.92
duckduckgo.com has address 54.229.105.151
duckduckgo.com has address 79.125.106.1
duckduckgo.com has address 176.34.135.167
You could now hard-code www.google.com to one of these IPs, but keep in mind that it will never work for https connections, because the provided certificates will (of course) not fit to the domain the user requested
Those are all specific cases where the domain that is redirected to has a valid certificate for the original domain. If we redirected just any domain to any other one, then there would be security errors because the server that you redirected to does not have the correct certificate for the one you originally typed in.