The amount of data that needs to be exchanged because of this approach is not scalable. Assume that there are 3 instances with 100 users each. Even if lots of users upvote/post/comment, the traffic is exchanged only between 3 servers. But if there are 300 single user instances, the amount of traffic/storage will be duplicated which can cause a huge load for everyone which might not be viable in the long run, for both the sender and receiver. PS: I am assuming that the instances periodically update content by fetching the deltas.