This may already be a feature that I am too smoothbrain to get working. But I would LOVE to let my client render 32 chunks locally, and then when the server sends chunks have them replace the client generated chunks. So you could truly have a render distance further than the server's even if you are exploring new chunks.

I have tried setting up a single player world with identical world gen settings to my server, renaming the folder to bobby-fallback, and setting my client render distance to 32, and bobby's max render distance to 32, and single player server view distance to 32. But I still only see chunks that the server has sent to me. but they do stick around outside of the server's render distance!

From my understanding, many servers hide the world generation seeds from the clients. Without the seed, it is impossible for the client to generate chunks that the server has never sent.

However at the same time it's really easy to reverse engineer the seed from world features. This isn't a problem most of the times.

most servers nowadays use server softwares like paper or similar ones, which have anti seed-cracking patches. so it actually is a problem most of the times.

A small serverside mod could be used to enable this feature by sending the seed to the client

Even a chunk pregeneration feature in a singleplayer world would be useful. Currently, there are no Fabric mods that allow you to dynamically generate terrain relative to the player's position. At least, I don't know such mods.