[plorkyeran]

It is almost certainly just something that hasn't been banned yet. There's a very long list of similar things which the UCI has banned, but they generally don't ban things which people might hypothetically do but haven't actually started doing yet, so each time someone comes up with a new idea there's a window of time to do it while it's still legal.

[MBCook]

I expect you’re right. It has to get on the radar to be banned.

To make matters worse unlike PEDs this may be very hard to catch.

It just floors me that someone who knew about the similarity between high altitude and partial CO poisoning not only decided to try it but got others to go along.