It was said on a call that Launch will have great migration features from DTM.
One of these features would be the ability to have launch use the embed code of an existing DTM property.
So can Launch and DMT share a staging library?
My thinking is this.
The planned functionality around the migration of embed codes is to migrate the production embed code from your DTM property to your Production Launch environment. The primary driver of this is the desire not to have to go to all the different IT teams that own the sites where this embed code is currently deployed to get them to update to a new embed code. It is assumed that updating embed codes in staging environments is easier to coordinate.
There aren't any plans to allow "sharing" of environments between DTM and Launch.