Voltaire, what you appear to be discussing is Racetech emulators & new springs, using the later generation BMW airhead fork internals. That ground that has been travelled before. While worthwhile for 70's bikes, that isn't waht is being mooted for the later GSs.
What Koko is investigating is several steps up from that, ie replacement internals - a true cartridge fork with externally adjustable preload, rebound, & compression damping. If these do as stated, then EUR 700 probably isn't too expensive cfw new forks. However compared to purchasing & modifying second hand forks that can do the same thing???? That really is the discussion point.
My '91 R100GS thread is here
My Ride photos are here
It's just better when there's twins involved....