I use GitHub nearly every day. In general, it's delightful to use and I've been impressed with the rapid pace of improvements, especially as of late.
That said, there's a handful of features that would have a big impact on my day-to-day experience. I'm cataloging them here with the aim of increasing visibility and prompting further discussion.
Disclaimer: It is not my intention that any visual designs be taken literally – I only hope that they may serve as useful source of inspiration.