Wouldn’t it be quite easy to implement this? Maybe not in a 100% secure way, but more like a 80% solution, where the user does get the template filled in, as the user pressing “reply”?
Or will that requires a backend plugin, which does provide the templates as extra context, if the user opened up the topic, and only have pot 40-45 in the viewpoint, resulting in the client haven’t and context about the “almost forced template” for the topic? 
I’m asking here, as I’m not that familiar with the component structure, but it should be a great addition, as mentioned before.