Not reinventing the wheel

Arte

I am probably not the first to seek these features. Do you know if these features or add-ons have already been done, or do I need to take a stab at them?

• Show top contributors in the sidebar (using a score that gives weight to more recent posts)
• Display site/category/forum/thread descriptions in the sidebar
• Unfurl posted links (as seen on Slack, LinkedIn, etc.)

Also, do you have a view on why these common features are not bundled with Vanilla?

• Signatures
• Polls

Bleistivt

Show top contributors in the sidebar (using a score that gives weight to more recent posts)

If you are looking for gamification:

https://open.vanillaforums.com/discussion/37990/yaga-for-vanilla-3-2-and-up

Yaga provides leaderboards which can be configured to show data based on "last week/month/year". I can't think of a plug-in that does exactly what you describe. It could definitely be done, however the post count alone is not a good metric. You probably want a leaderboard based on quality not quantity.

Display site/category/forum/thread descriptions in the sidebar

You can use messages (dashboard -> moderation) and if you want to go further pockets (plugin included in Vanilla) to add text to various places in your forum.

Unfurl posted links (as seen on Slack, LinkedIn, etc.)

The rich editor (included plugin) does that for you as you can see above.

Also, do you have a view on why these common features are not bundled with Vanilla?

Signatures

Polls

Signatures are viewed as a somewhat antiquated feature you don't see in modern community software very much anymore. But it is an officially maintained plugin, so if you need it, you can install it.

Polls are not part of the open-source offering, but there is an open source alternative.