I've been using git spice (https://abhinav.github.io/git-spice/) for the stacked PRs part of graphite and it's been working pretty well and it's open source and free.
GitHub have proven the ability to execute very well when they _want_ to. Their product people are top notch.
Given the VP of GitHub recently posted a screenshot of their new stacked diff concept on X, I'd be amazed if Graphite folks (whos product is adding this function) didn't get wind of it and look for a quick sell.
This was "announced" in October, and last week they were saying they're shipping to trusted partners to kick the tires before a real release, with posted screenshots.
So, we'll see what it ends up like, but they have apparently already executed.
Woahhhhh I missed this. Got a reference or link? My Googling is failing me. That's my biggest complaint about Github coming from Gerrit for Open Stack.