A friend has been trying to make slot like through-hole pads. These are the kinds of pads you’d use for the strain-relief pads on a USB connector etc.
I don’t use these, but I should and probably will on my next board. My friend had ran into fabrication issues using the oval drill shape in Kicad. Investigating this I found that the oval drill don’t seem to get written to the excellon drill files by Kicad. So there’s likely no way that they’d get fabbed (my friend uses the OSHPark Kicad import, but I’m guessing this just generates the drill files using Kicad anyway).
From what I understand of the OSHPark documentation on the subject. These holes should be marked as internal routing. In Kicad this is specified in the Edge.Cuts layer. The image above show an example where I’ve marked the routing around the hole. I believe this /should/ be fabricated correctly, but need to try it out. The OSHPark docs contain the following image (which they say /should/ work and will result in a plated hole: