One implementation specific detail which makes Karpenter interesting on Oxide is the tunable CPU and memory parameters rather than strict instance type shapes. The prototype I built for Karpenter on Oxide generates all possible "instance type" combinations, so you can create some really specific nodes to bin-pack pods.
Another interesting area is multiple providers. This is becoming pretty common across public clouds too. A multi-provider Karpenter is something I'm interested in and I know some folks have already been gluing together, but the Karpenter story isn't great on maintaining those since you basically need to compile them together today. CAPIs multi-provider story is a bit cleaner since it only relies on CRDs.
If you have ideas, let's chat in the Kubernetes slack #karpenter-dev.
Autoscaling is a requested feature, and Karpenter fits that shape naturally. The nuance is to decide where something like the Cluster API provider ends and Karpenter begins since there's a bit of overlap in concerns. Specifically, both want to manage Kubernetes nodes but for different reasons. We're discussing it though. We have a Kubernetes watercooler meeting today where we'll likely discuss the comments in this post!