I really like the extended tube design
Makes a lot of sense - I wrote to Saracen way back for them to do that but they ignored me. My other suggestion it to attach the cable stops to the head set tube instead of the top tube - means less outer cable is run thus more lightness.
With ISP (Integrated Seat Post) the frame can be made lighter and/or stronger since there is no overlap of seatpost inside the seat tube. The downside is the frame is cut to rider size but if you get that right, then it does not matter (seats and pedals can make up to 20 mm difference). Obviously you can only sell the bike to someone who is same size or shorter than you.
Someone mentioned that the seatpost cannot be dropped - when I was buying and reading mtb spotters monthly, they mention to do that on decents but in all my years of riding, I've never doene that, in fact a lot of my seat post binders are not QR. ... whcih may explain why I am crap at downhilling but hey ho, I get there in the end.