Next Runner Auto-scaling Architecture | GitLab is their plan to move away from their fork.
They are working on a replacement centered around a new library named Fleeting. It’s being developed in the open at fleeting · GitLab and they have a large-scale tracking document Docker Machine Replacement Project Plan (&6995) · Epics · GitLab.org · GitLab showing that they plan to finish by Q2 of this year.
It’s interesting that they plan to effectively drop most of the 20+ cloud providers that docker-machine currently supports, focusing on “the big three” and encouraging the community to contribute plugins for other providers. That epic posted above shows someone two days ago who was concerned about Hetzner support, so hopefully that’ll result in a driver that folks can use. As a heavy user of DigitalOcean, I fear that I’ll have to write my own driver before giving this a spin. 
That being said, I do hope to poke at it a bit over the next few weeks – if anyone else gives it a try, please update the topic!