Is it possible to have player (end-user) enabled Machine Learning? For example in my game Follow the White Rabbit it would be helpful to adjust the model. For example supporting different hand sizes, skin tones, as well as support hands that had more/less than the standard number of fingers.
Yes, you can adapt a model on-device using any one of our ML frameworks, including Core ML, Create ML Components, MPSGraph, and BNNS. The approach you take depends on the data and problem you are working with.
To detect hand poses, I recommend checking out the sample code project Detecting Hand Poses with Vision.
If you foresee training on a small dataset, then it might be worth looking into using the KNN algorithm available in Core ML, check out the sample code project Personalizing a Model with On-Device Updates to learn more.
Finally, it is worth browsing through the documentation for the newly release API, Create ML Components.