Negentropy / time syncs are not optional, IMHO. We will have to add to the mandatory core of Nostr if we want to scale this. We can't keep downloading everything over and over again just to check if the local instance has all the data it needs. 

I am getting more into DVMs that return a Snark/Stark proof these days. I think it could provide some interesting possibilities for verifiable computation. 

If you have the IDs of the events you want to include locally, you can send the IDs alone for a verifiable DVM to compute and return with a proof that it did what it was supposed to do. 

It gets even better if we can add some homophobic encryption to event data. 

Future is bright.