Integrated graphics is getting better and better as time goes on. nVidia even dropped the m on all of their mobile products as they say the difference is so small, it doesn't matter.
While external graphics are nice for upgradability, upgrading and laptops are normally mutually exclusive. There are exceptions, there are graphics cards you can sometimes swap out, but it remains pretty much the same, they are not meant for that.
To be honest, though, grabbing a notebook with a 1060, 1070, or 1080 should last you at least ten years on CAD, and I am surprised that your current device isn't good enough for that.
Heck, even though my experience on CAD is minimal, I would have no problems using modern CAD software on an FX-55 with a GTX 7800.
Just some thoughts.