I just learned of this channel via your post. I am blown away by some of the tutorials I've watched and his skill. This is really too bad that he won't be doing any more. I wonder if there was an issue with Apple. Not sure why there would be, but he mentioned that some Fusion tutorials may appear on that channel in the future. So he's only stopping Motion tutorials while I suppose he familiarizes himself with Fusion.
This is really sad. I don't know anybody else that is able to show the potential of Motion like Mr. Ubsdell did. A great master of his craft and – that is not to underestimate – with a great voice and articulation for such tutorials. A source of great value! From what I know about Motion, at least 50% I learned through Simon Ubsdell (and 20% through fcp.co).
It doesn't look like he is "shutting down" his channel, nor pulling existing Motion tutorials. It looks like he's just not going to do anymore. Which sucks. But you can only go so far, with an app that hasn't had any major upgrades to its functionality in a very long time.