Indeed, using the diff on the client to send just the changed data might work. The only thing I dont like, it the in-ability on the server to process the data in any meaningful way. For your Elixir app this data is just a binary blob without much meaning. It really depends on the use case, for some apps this might be OK. My use case requires some insight into the data on the server, so it wont work out here. BUT… Still great, in case the server should stay dump and clients just exchange data.
Lots of good ideas floating around! 
