So it's a non concern. There is nothing additional an app can do, anyone concerned should already be concerned with the relays they are connected to anyway.. IMHO.
Discussion
having a caching relay connected over Tor would help for untrusted clients, needs to have auth pass-through also
would also save bandwidth as well as increase privacy, with Tor or without, as it cuts out a lot of time correlation if you control the cache relay
this is why really all clients should have the capability to use at minimum a local cache relay for storage and optionally a remote one (for more privacy)