Because Flarum is a Single Page App, we don't have the bottleneck of downloading redundant HTML on each page load. We're already loading the strict minimum from the API.
Technically, a predictive API request system could be used to speed up Flarum's navigation, by loading discussions before you even click on them for example. But such a system is not easy to implement and could create issues with some extensions. I'm also not sure whether this would bring a significant performance improvement.
Probably the best performance improvement we could implement is javascript code split, so that we load only the minimum amount of code at initial page load, then load additional script files once they are needed. This would greatly improve the initial page load time on slow connections and allow for the use of more extensions without too much of an impact on the initial page load.
