As @wycats mentioned, there are a lot of improvements coming in this department but I thought I’d jump in with some thoughts on client performance.
Right now, if you throw 10k rows at Ember without thinking about it, you won’t get good performance for free. I am not convinced this is a problem outside of synthetic benchmarks, but I’d love to be proven wrong with a real world example.
Having said that, it’s not impossible to deal with that much data in Ember, you just have to think about it. People often tell us Discourse is a fast app but I honestly haven’t spent much time making it faster. We have nice little rendering statements that output how long in ms a view is taking to render. If we find something is rendering slowly I’ll dive in and usually find we’re creating too many views or bindings for data that never changes. Removing that is quick and performance bounces back.