Today when editing a canvas app you are looking the whole app from other potential owners/builders. This makes it very hard for app makers to share a build. We have experienced many times that developer 1 having the app open and forget to close it which then makes it impossible for developer 2 to edit until the app times out (8 hours). Because we are global company with offices in 74 countries the time difference could potentially create the scenario above because we are unable to get in contact with developer 1 because the person is a sleep. 8 valuable hours are at waste. From a productivity standpoint I would say that co-authoring also would carry a lot of positive standpoints with it. I definitely see the need to lock editing down so you don't mess up things but as in Excel, you lock down the cell you work in rather than the whole workbook. Why not lock the screen you are working with rather than the whole app itself.