There is a site called 500px.com (for showcasing photographs) that I feel you can draw a lot of inspiration from in how it draws you in and help promote an engaging community. Here are a few crucial features that I feel will elevate itch.io as a platform.
1. I propose a Discover-feed on a subsection of the webpage similar to how it works on 500px. It will show a feed of content - screenshots, gifs, videos that can be liked, favorited and commented on. And also a quick button to follow the project to which the screenshot belongs to. This encourages indie developers to put up more content and link to said content in their twitter feeds, homepages, etc. If indie developers catch on you suddenly have an enourmous stream of content continously added that draws people towards itch.io. Discover feed would look like:
Why would indie developers want to link to itch.io? For the simple reason that people can:
2. Follow - this is HUGE. There often is no way to follow the developments of indie projects and if itch.io can fill that gap I think both consumers and content creators will be very drawn to it. When you follow a project you either gets updates for milestones or every piece of content put out - depending on your options. And you can also choose to be emailed e.g. on milestones so you get notified on important things like releases.
3. Inbox feed that shows people who likes and favorites. In the top menu it should show when somone likes or favorites a content you've put up: "User X liked picture Y" with a quick link to go to that user's page and like their content if they have any - this creates this nice engagement where people support and help promote each others content. Also everyone likes that kind of feedback and encourages putting content out there for other to like and favorite.
With a discovery feed I will be encouraged to keep coming back to itch.io to check out the awesome content people put up and be inspired. This is a win-win for both content creators and consumers.
Oh and one thing I almost forgot:
4. Following-feed, a feed of content from the projects that I'm following.