The way to solve the metadata analysis problem is to flood the network with noise. Every time you DM, create a whole bunch of automated junk DMs at the same time. Like an anonymity set.
Discussion
That is one approach but you could also just not use Nostr and use an onion routed network of Lightning node.
You get spam prevention (sats payments) and you never leak metadata in the first place. You also don’t impose undue cost on relay runners that would have to host all the junk data