nout on Nostr: I think having a caching layer is ok for performance, but that layer becomes attack ...

I think having a caching layer is ok for performance, but that layer becomes attack vector as soon as your application gets bigger or the layer gets smarter.
A bit different approach is to consider using independent caching services or providers. Some that you have no direct relationship to, but your app/architecture just uses them. Even better if the users can actually select this somehow.
This is of course way harder to implement, but on the other hand it's presumably more censorship resistant.

To be clear I appreciate Primal and I'm using Primal right now on desktop (I have not found a better client on desktop), but I'm afraid the architecture and incentives may be pushing Primal in the wrong direction in the future.