Yes, then you could make it editable from the start and if people add rounded corners to it then turn it into a non-editable path.
There is of course a more general solution, in which you can edit the path from the start, move the vertices around and still be able to apply rounding on all corners points that have collapsed tangents. The path could be changed from a rectangle to a trapezoid or another polygon and then rounded. After that you'd still be able to move the corners around and the path rounding would update accordingly until you click Convert to Curve. Once you do that it expands the path and you and the corners are not interactive anymore, you move them they lose tangency.
Adobe does it pretty well, except for when you move the rounded corners around. Then the path loses shape.
This plugin does it right, you might want to check it out: http://www.astutegraphics.com/software/vectorscribe/ ----> Dynamic Corners Tool
Hope this helps.