Do you see any problem? Where's the "issue"? Two calendars (with two different URLs) are available, two calendars are shown.
The issue in my particular usage is that DAVdroid behaviour is inconsistent with other CardDAV/CalDAV clients in use. For example, with CalDAV Synchronizer (Outlook client that does both CalDAV and CardDAV despite its name) and iOS, when authenticated as user1 it will only allow you to view data that is available under user1's account. For this reason after user2's calendar is shared to all users, user1 will still need to "subscribe" which adds user2's calendar as a synced copy into user1's account. This allows other CalDAV clients to view user2's calendar using user1's credentials.
It also seems that the CardDAV component of DAVdroid acts in this manner. When user2's address book is shared to all users, it does not appear under available address books when logged into DAVdroid using user1's credentials. When user1 "subscribes" to user2's address book within SOGo then user2's address book is shown in DAVdroid.
I do not have much experience with WebDAV servers/clients, and my experience is limited with SOGo, so I don't know how the other servers handle sharing of calendars/contacts, but in my environment it seems that the DAVdroid 0.9.x behaviour made more sense.
The other thing with having the two copies of the same calendar (one from user2, one from user1's subscription) is that although the url's are different, they have the same name. Functionally it doesn't matter which one you select within DAVdroid as they are effectively the same calendar, but it is quite confusing.
I can see that you consider this to be an upgraded feature to the previous behaviour in DAVdroid 0.9.x, and in some usage cases it certainly would be. It would eliminate the need to "subscribe" to the calendars under user1's account for them to see user2's calendar. However it could get very confusing and possibly expensive? if many users have globally shared calendars, which would be shown in each user's list. Perhaps if there was an option to disable this feature to switch behaviour back to the way it was in DAVdroid 0.9.x then it would make it more user friendly? (I'm not a programmer so please don't bash me if I'm making an outrageous suggestion...)