On mobile side of the new Edge. It respects Page Visibility API what is common thing on video and other media content sites. PVA is a way to tell the player (inside of a page) that the device don't anymore see it and then it pause the content playing. That means no background play.
PVA is a web standard, but if it give end users bad experience, then we need to give that user a option to disable PVA behavior. Only way now for users to use background play is to load desktop version of the site and run the player from there. Then it start to have performance issue and that is one what we don't want.
So can devs for new Edge take this a something what think about.