When browsing a forum, I notice that a topic size can become overwhelming due to a massive amount of replies. This can get annoying navigating sometimes so I thought perhaps an option to expand to the list of replies could be added, where as it would just list the initial post at default.

Small point but I thought I'd just throw that out there as an idea.
In the Preferences, you can select from Topic View, which has a master topic that expands to a topic system. The thread structure is still visible at the bottom. This does load a new page, and if you're used to each post being individual it can take some getting used to. There's presently no way to keep the thread view and expand or collapse that view directly, although that might be an interesting feature in the Next Big Forum Overhaul.
In response to Jtgibson
All views except the Topic View suck anyway, to be honest. And so does loading one post per page. Why are the default settings like that?