Put HE (dns.he.net) in your back pocket - they run a free DNS service which includes slave (do we still call it that?) service so that you can add their resolver as an ultimate failover / failback if your self hosted DNS takes a dive for whatever reason things break in our world.
Generally, hosting your own DNS “should” mean having a primary and secondary on separate AS networks, or at least different provider routes or locations. But if you’re doing all this from home, where is the second location for DR purposes… exactly? I sure don’t have one, power goes out here everything goes dark - in the old days everyone used to do this (share out tertiary DNS to each other) but it’s become a thing of the past in today’s world. HE can help fill that gap.
To your point - I use Gcore DNS and Bunny DNS for my stuff, as I mainly use online VPSes and don’t run racks of hardware at the house. The only things I physically selfhost at home are a pair of old laptops acting as storage servers which backup all my bytes and bits from online to some SSDs.
There are already instances doing this (and Mastodon ones as well), it’s a thing - there are warehousing no-user instances[1] But they could be blocked! We can’t have that, luckily…
…the Lemmy API and RSS feeds have no authorization around them for consuming the firehose of data; if I were a person doing this data gathering, I’d just passively monitor the firehoses off the top instances from random rotating IPs. Could and is most likely happening right now, can’t block them.
[1] I personally wrote a simple script which uses the fediverse observer info, grabs the XX most popular communities and builds a subscription import file to bootstrap a new Lemmy instance. wasn’t hard, just some curl and jq work.