I can help you to make plugin for reverse chronological order of posts. Before I like to share other possibilities to resolve this problem.
Instead of displaying all posts in reverse chronological order you can land users on latest post on topics. For example, If a user already read first 1-6 posts on a topic and after he came back when the 7-9 posts are created then currently Discourse landing him on 7th post URL (like /t/topic-slug/1/7). Here instead of displaying 7th post we can simply land him on 9th post like /t/topic-slug/1/9 (by clicking the topic link). So there is no need for user to use shortcut key or scrolling to reach last post.
Else we can display a button (better to display on hover event) saying go to last post next to the topic title. So if user clicked the topic title it will go to 7th post else if he clicked our button we can land him on 9th (last) post.
If you still think reverse chronological order is the better way then I will check it and tell you soon about how much it is easy and possible.