I think that requirement only applies for the first 8 weeks that they are on sale. So, should one pre-order or wait for the fire sale? The Hornby 2-BILs started at £129 but can now be had for as little as £59.
Judging from what happened with my E4, pre-orders would go out at the high price, without emails notifying customers of any price rises.
There might not be a big fire-sale, though. For example, I haven't come across any significant reduction in the price of E4s yet, certainly not at Hattons.
Although I am not wildly happy about the price, the Birdcage Stock would still be a reasonable option for me, compared to the Kernow Gated Stock and the Hornby rebuilt ex-LSWR 58' coaches. I was going to get both the Gated Stock and the Birdcage Stock, but am now considering getting the first option to become available, and forget the late-comers.