It would be nice to be able to trigger a flow when a new person subscribes to your channel.
Basically I would like to make a flow where if a person subscribes I would paste a message on our facebook wall with the name of subscriber.
Thanks for the idea.
But currently this is not achieveable through the available triggers added for Youtube in Microsoft Flow:
There are APIs available to get the subscribers information for your Youtube channel, which would reqiure some additional knowledge for building Custom APIs:
Further, please consider submit this as an idea in the Flow idea forum, so that this idea would be considered by the product team in future release.