"Sledgehammer" is definitely the word I'd use, but it is an interesting thought. The Agora seems like it'll be plenty for the foreseeable future, but there's a hypothetical future where we outgrow it and need something that scales better.
At a quick glance, Decidim seems like it would be a decent solution if/when we need to upgrade. Free/libre with a focus on transparency is a great start, and it looks like the tools are pretty flexible.
But as a counterpoint, there's a lot to be said for keeping governance here as long as it's sustainable. Removing as much friction as possible from voting means more people will participate, and it doesn't get much easier for voters than dropping an "aye" or "nay" comment on a ballot post.