Not as such. What I am saying is ...
... there are countless things (and not all even electrical) which we know "go on fire from time to time". For each of these, we ideally need to consider (a) whether the magnitude of the risk is high enough to warrant consideration of doing anything to reduce it (life is full of very small risks, and we do not, and could not, feel it necessary/appropriate to take action to reduce all of them) ... and (b) if we decide that the risk is great enough to warrant consideration of 'action', then we should decide whether the magnitude of the risk, in comparison with other risks, deserves action about it to be prioritised over action in relation to other risks.
In the case of the CUs, I'm personally not convinced on either count. In terms of (a), I admit that I'm not too sure, since I really know of no statistics about how many house fires originate in plastic CUs. However, as for (b), I would be surprised if there are not much more common causes of house fires than CUs, so would prefer to see those other causes addressed before we even thought about CUs.
I realise that you are confronting me about this because it was me who 'brought it up', but I am sure you are aware that many people (including many electricians) share my scepticism about the 'need' for 'non-combustible' CUs.
I have several in my house, all plastic, and I'm perfectly happy with that.
I personally don't care whether mine are plastic or metal, since I am confident that I would do nothing in a CU which would present a significant risk to me, even if it were metal. However, if the reg didn't exist and I needed to have CUs replaced (for other reasons), I suspect that I would probably stick with plastic.
Kind Regards, John