Hello Team Sansar,
After many years, this is still not seriously get the focus.
refer to this 2017 community/posts/115000814847-Collaboration-How-do-we-work-in-teams-
Maybe good idea to include it only for payed subscribers, for sure lot of free subscribers will upgrade to at least Creator!! so that at least one of the team-member (owner), can give access to free and payed subscribers to work on the environment. You as team have already so many experience with second live... and many of us, don't understand why it is not yet included.
We (all Sansarians) hope it will be VERY soon possible!