Nothing super fancy, but clearly useful to our team (I'm sure to others as well). It would be really useful if we could have an explicit obvious alert (a popup like what Excel does in these situation) when opening a ArcGIS Pro project (.aprx) if the project is already opened by someone else.
Our team works on a lot of projects and sometimes, more than one person can have something to do in certain projects which can already be opened by another teammate. The mention [Read only] in the top bar is not always something we see and we can make a lot of change before noticing it.
The read-only feature is alright, just the notification that can be made more obvious to users.