Yeah and lots of 4k players don't play anything higher since their keyboard don't allow more than 3-4 keys at once, yet the rule wasn't pushed that far. That issue is mostly rhetorical, anyone who was willing to spend the time required to reach this level shouldn't be against the idea of throwing down 10$-20$ for a keyboard with nkro. If they for some reason they can't, then they understand their limitations and won't try to push their problems onto others. Most old ps/2 keyboard are cheap, got no input lag since the signal doesn't go through the usb drivers and are nkro. The limitations or bugs mentioned earlier are mostly due the usb interface, no need to buy anything expensive...
Goes without saying that I'm 100% against anything between the lines of "mappers are not allowed to do this because of this and that". It's like saying an artist isn't allowed to use the color green because some people might be colour blind. Anyways, this is a whole different issue.
But on this point, this rule is only a ranking criteria. There's no rule about the unranked songs on the servers needing to have less than 7 simultaneous keys. I'm pretty sure the same logic can be applied to this mod, since it's also unranked. Also, these patterns can easily be made without 7 simultaneous keys so these patterns can still end up being ranked, and they did.
So, having a way to train these is still something greatly helpful and I don't see this causing any sort of contradiction.