Also this forum post, which gives me confidence that dr.dimitru cares about keeping the package up to date and continues to explore how well it works with new features.
For the original FlowRouter, I believe you can put a dynamic import in the action() hook and render the template with .then. A loading screen should also be possible by rendering before the dynamic import.
The other extras that ostrio:flow-router-extra gives you are just very handy to have too.
Are you aware of a way that the original question would be possible with FlowRouter?