I've never used this tab. (Just opened it for the first time.)
It's cool, and I'm disappointed to see it go.
BUT: We should spend a minute thinking about the counter argument. Little and unused features can add cruft to a codebase, and significantly impede development. It's possible that hooks for corner cases and features can be so complicated that working around them becomes more burdensome than supporting the important use cases.
Case in point: When I was lead on Syncplicity, we had a corner case where a given folder on disk could be in multiple synchronized folders in the cloud. (Long story.) The problem was this corner case made many use cases, in the desktop client, significantly more complicated and bug-prone than needed. (What happens if you have different permissions to the same file?)
There was a point where I put my foot down (as lead) and said we couldn't support the corner case anymore. This lead to almost a year of two branches of the product, and daily merge conflicts between both branches. I had to put my foot down again (as lead) and push that we had to ship the version of the product that didn't have the corner case and stop working on two branches.
This makes me wonder if Github needs to cut back on corner cases and other little-used features in order to fix some maintainability issues?