I agree with you both here and the snipped bit further down. It is the case (as you say) that legal precedent, which will define the law in detail, is yet to be set. My point was that I bet (if you like) that the covert intent is to discourage DIY and that, given that, when legal rulings are handed down, they will slant that way. You are right that it isn't and cannot be said to be definitely illegal to DIY gas work unless CORGI registered *yet* as the law has not been refined. I suspect (and said) that it will *probably* turn out to be illegal.
The unfortunate thing is that it will be (in the end) DIY work that was neither competent or "competent" and which causes death or injury (ar, at best, significant damage) that will trigger the legal ruling. This too will slant the outcome. No-one is going to take a competent person to court for doing a proper job even if they aren't "competent", I suspect!