It would be fantastic if Designer eventually had Trim, Fillet and Chamfer line editing tools as found in all CAD software.
I am not suggesting that Designer should ever become some sort of CAD hybrid application but merely suggesting that these tools are invaluable when dealing with parametric 2D lines. They save a lot of time and effort.
People have been asking for these to be implemented in Illustrator for years. Hopefully a dynamic team like Affinity can grant this long standing wish.