tl;dr Alyssa Rosenzweig. Amazing news, she's been a driving force behind reverse engineered GPU driver project Panfrost as well as had part in the Apple M1 GPU driver. I was surprised to hear that she was leaving Collabora but it makes sense that she'd end up at Valve. Hoping for great things in the PC GPU space from her!
I am a bit surprised by this as her expertise really isn't in optimizing AMD driver performance, which is what Valve has been mostly doing.
I suspect it might be related to the rumored Decard VR headset that supposedly includes some ARM components.
If she were to reverse engineer the Qualcom VR stuff this might even result in a open-source driver for the Meta Quest headsets, which would be fantastic.