Did you notice the on the fly combination diamond wire and downhaul adjuster?
http://user.tninet.se/~zdt420t/barcelona/fittings3.htm
I believe some of the BIM "A"'s also have incorporated a system that automatically increases downhaul with increased mainsheet tension- I believe it worked along the lines of the "headknocker" system on the boom recently discussed in another thread here except the tail of the mainsheet fed into the downhaul so increasing tension on the mainsheet pulled the downhaul on.
I've attached a photo of the system on my old 18sq. A modification of the system on the A's with a single swivel cleat with double-tailed line (cheaper and lighter).

Kirt