Lol! I wrote an article on this in National Kart News a few years ago & created a pretty big poop storm… Yes, it happens. And the EDM expert I talked to showed me a chart with different ‘textures’ he could cut too & assured me we could “hide” the EDM process rather easily.
As Dan said, a simple rules change eliminates this… Simply say “blowdown has to be between X & Y and we (sanctioning body) don’t care how you get it there.”
Research I did shows machining a cylinder would add $150 to the blueprinting costs and eliminate the need for EDM and/or the “pot luck” or search for a “national cylinder” ( adding $600-1500 more in costs). Also, I never remember “blowdown” being an issue with the old open Pipe engines…
So to answer the initial question: yes some people do/did EDM cylinders and yes it makes a significant difference on Supercan motors.