It's not featured, and I wonder why? It's a very useful and important community post. I personally think it should be permanently featured like sandbox. (however like the sandbox, it's sometimes edited and thus bumped). But still, shouldn't it be featured?
No it shouldn't be featured. There's only so much space in the sidebar. I think 4 or maybe 5 questions is the maximum. Occasionally one of them is a blog post and/or a feature post on Meta.SE. Then the sandbox is permanently featured. And we've occasionally got another important announcement that needs to be featured. That leaves one lot for regular "hot meta posts". As neat as the bounty post is, I don't think it's important enough to take up another slot. It's something that is only really relevant to PPCG "power users" who are looking for an extra challenge, and these users are likely active enough that they've found out about the bounty list on their own.