Personally I don't think PCIe riser is ugly. It is the PCIe riser that makes the A4 its layout possible.Don't need to take this seriously at all, but I always felt that the plug-end of the PCIe extender to be particularly ugly. In this case the power cable is also visible at that position. I was wondering if the flap for the power button was extended, it would really nicely cover these two aspects. Perhaps the the extra real estate can be used to house an USB-C header or something?
If you really don't like it ,you can add a screen or a panel to cover the riser.
Thanks for your advice anyway, your drawings are quite interesting.