Every once in a while I think of creating a little DNS cache that never expires entries, except when it runs out of storage, and run it on a Raspberry Pi, feedi

Every once in a while I think of creating a little DNS cache that never expires entries, except when it runs out of storage, and run it on a Raspberry Pi, feeding it with DNS queries on my home network (but never using it to send replies to clients, just store queries and results). But I never do anything about it.