I've noticed the Google Tag Manager tag in the Tag Marketplace for a couple months now. It appeared with little fanfare. I have a use case for it coming soon, and I'd like to learn more about it from Tealium employees and fellow TiQ users....
So far I've browsed the template and it seems rather flexible/straightforward, but I'd love to see additional documentation and/or discussion.
In my experience, we have used the GTM tag to assist customers who are migrating from GTM to TiQ, either so that they can migrate tags from GTM to TiQ and then easily remove the GTM container when they are ready.
Alternatively some customers that have specific reasons that mean they 'must' retain GTM on some sub-domains or for certain inbuilt hard-coded tracking events, but they still want global control of all of their tags from TiQ.