But when you’re talking about sending a lot more data to clients, you really need to consider what that means for the internet bill of instance owners.

I would argue the opposite, actually. A lot of this data could be distributed in a p2p manner and the client nodes would have to rely even less on the servers. The key part would be that this data would have to be self-authenticating, but we do have the mechanisms to do that (Linked Data Signatures)