Since multiple model builders can (and do accidentally) end up opening the same page for editing, when one saves, and then the other saves, someone gets their work lost.
It would be very helpful to have an indicator that shows up on a page that would shows me when if someone is already in editing mode on it. I imagine this could be something really simple like a "!" mark on the page's title when someone has the page open for editing (see my example image below)

If I was to get really picky, this indicator should only appear to people who are assigned page builder access, not for all users