If you know which car you want I’d order now, you can always cancel if you want to. And if the AP drops in Jan then it’s a 2 min job for the dealer to re-submit the Motability order at the new price.
I’m not sure which car that’s why I waiting for Q1 to see any new arrivals or price changes yes of course dealer can cancel order but I’m taking the gamble roll on Tuesday 2nd January