This is tricky for Firecracker, both because of security (and the attendant switching costs of keeping exactly one VM connected to a GPU at a time) and because of the Firecracker tenet of supporting oversubscription. They've been talking about it for a couple years. I think they're actually talking about forking off a GPU-capable variant of the project to work around the drama.
No support for PCI devices at the moment, but I believe it's planned for some point in the future.