That is a very good question indeed... Now that our status miles from the previous 6 months show up again (I had just requalified 5 months ago and already did 22k new status miles in the 3 months following the requalification - they all had finished after the status extension but reappered today), I was asking myself the same thing. Status validity is one thing, but I could imagin all the 3 scenarios shown in the nice graphic above.
While I hope it'll be scenario 1, it might just be a rolling 12 / 24 months as always.
It might be Nr. 3, so if we hit the 40k during the next 6 months all would be fine, it might be Nr. 2 (achiving 40k during the next 6 months won't help, since they only look 12 months form now and everything before that would have expired by then), so I hope they'll clearify that for us. And I hope it'll be scenario Nr. 1
and there might be a scenario Nr. 4: you get a rolling 12 months during month 1-18 as new first year, so it would not be JUST 2 or JUST 3 , but any one of them or month 3-14, 4-15 and so on....