Regarding the new order/ quota system. Its been on for 7 months at least at the Hermes on Sloane Street. You have to be very specific and choose leather, hardware, colour and size all upfront and your wishlist is then uploaded and has a timer for 8 months. If you are unsuccessful you have to come back in and 'refresh' the online request.
I ordered a Hermes Kelly 28 Sellier in Noir with Ghw in Epsom approx 8 months ago and it came in about a month and a half ago. I was surprised I didn't have to wait that long as a my SA in louis vuitton Harrods had to refresh their request 3 times.
On a side note scoring a Birkin, Constance or Kelly in Sloane Street in nigh on impossible, all stock is reserved for clients and those who ordered. You might have a chance if you go at opening as that is when clients come in and collect their bags from the manager etc..