bob2 depending on how much time you have and can invest on getting to understand Flarum and writing the extension(s) (and possibly quite some dependencies) you should be able to get the extension done before stable. The next imminent release is beta 7 which is not yet completely backward breaking.
As to being able to work with page mutations.. If you are able to write the extension properly yes, most of what you do is logic in the frontend/js framework side. Flarum should be able to handle it properly although it has not yet been properly tuned for mass traffic. In the end the core team and community are open to assist with any feedback you have, even though implementation of fixes might need to wait for any upcoming release.