I do not know the exact number, but it is likely to be > 11.7k.
Here is the theory:
If the top 1% of all diamond members is 117, then the bare minimum number of diamond member is 11700.
That is only the minimum as diamond plus is actually the top 1% by revenue. Then you add on diamond invitation, corporate deal etc.
Another way to look at the stats is the average frequent flyer numbers worldwide. There was an article somewhere mentioned that about 5% of the travellers travel 100k miles or more per annum. It is more realistic to think that in all cx travellers, at least 4-5% are diamonds.
It is only my estimate, but I am happy to accept your point of views on this matter.