When a user is changing ownership of an item, they should be able to do so, regardless of whether the item is shared with a Shared Update group or not. As with regular groups, if the recipient is not a member of a Shared Update group with which an item is currently shared, then changing ownership should fail with a similar error.
We have thousands of users in our org. They all have the privilege that enables them to create Shared Update groups and to transfer ownership of items; they are the ones that know what is going on, not the ArcGIS Online Administrators, so expecting admins to handle these sort of things does not scale.
Many of our users are working on work collaborative projects for which all members of the collaboration have equal responsibility (the differences between being an owner of an item and having access as a member of a Shared Update group is a related problem.) They use Shared Update groups to work collaboratively.
As people move off of these collaborative projects or move on from the organization, it is important that they can be off-boarded quickly and easily. That currently involves having to transfer ownership of relevant content to others remaining in the collaboration. Again, it is the users who know what needs to happen, so it does not scale to get Administrators involved. (It would be great if groups could own content too, so that this kind of ownership transfer was not always needed, see Allow Organization and/or Groups to own data in AGOL and Enterprise.)
It is un-intuitive and time consuming to perform the workaround of having the original owner un-share items from Shared Update groups, transfer ownership, and then have the new owner re-share items to the same Shared Update groups.
This specific Idea has come up before, as part of broader Ideas, so I wanted to explicitly separate it out for consideration. For example, Enable Content Manager role by improving/fixing item sharing options and interfaces (see point #2), and Improve Groups where members can update all items and documentation.
