How would it be different than a client or solve the issue being stated (not seeing that many of your posts)? It seems to me that Nostr conversations (notes) have a lifetime of 30 minutes to 1 hour max. After that they rarely get seen or engaged with.
I don't think that's a problem. It mirrors the real world and conversations we have with people. Our conversations don't linger in the air for days so anyone else can walk into them and pick them up. It's an in-the-moment (or, in Nostr terms, Event-driven) model.
For those people you absolutely don't want to miss, NostrGram (for instance) allows you to create custom lists. You could just put the "most important" people into a list and load that list so you don't miss anything.
I'm certainly open to any other ideas though. I'm all for anything that makes the user experience better.