@Sekomu Thanks very much for the pull request, sorry that I missed that you already sent a CLA in the past!

We have merged the pull request and added some improvements on top of it, e.g. added single frame preview as well via a Fixed Track Time parameter. This has been requested in this issue ticket.

From the changelog:

Added experimental EditorSkeletonPlayer component to allow Editor playback of the initial animation set at SkeletonAnimation or SkeletonGraphic components. Add this component to your skeleton GameObject to enable the in-editor animation preview. Allows configurations for continuous playback when selected, deselected, and alternative single-frame preview by setting Fixed Track Time to any value other than 0. Limitations: At skeletons with variable material count the Inspector preview may be too unresponsive. It is then recommended to disable the EditorSkeletonPlayer component (at the top of the Inspector) to make it responsive again, then you can disable Play When Selected and re-enable the component to preview playback only when deselected.

New spine-unity 4.1 and 4.2-beta unitypackages are available here as usual:
https://esotericsoftware.com/spine-unity-download

@Sekomu Awesome, thanks very much for sharing!

Sekomu (If possible, I think it would be great if this feature could be officially adopted into the Spine Unity Runtime )

We would be happy to include such a component in the spine-runtimes officially (potentially with some slight modifications)! Could you please send us a signed contributor license agreement (CLA) to contact@esotericsoftware.com as listed in the Contributing section here:
https://github.com/EsotericSoftware/spine-runtimes/tree/4.1/#contributing

@Sekomu Thanks for reporting and sorry for the troubles! We could reproduce the issue on our end, in both spine-unity and in SkeletonViewer.

We have created an issue ticket here where you can subscribe to receive notifications upon any updates:
EsotericSoftware/spine-editor753