What exactly is being referred to here by "a more compliant strut"?
More compliant valving? Or a different strut design that doesn't suffer from the problems the KYB/STi struts presently seem to be suffering (i.e. bouncy ride on smooth roads, clunking sounds, stiction)?
On the valving side, what could be improved? I would say that the multiphased valving presently employed in many of the KYB/STi inverted struts (i.e. Ver 5, Ver. 7) does a very good job of absorbing the rough stuff (when functioning correctly), while still providing a very sporting ride.
If it's a different design, that doesn't suffer the ills of the KYB/STi design, what evidence is there that Bilsteins would be the answer? What is it about there design that would offer better performance over the KYB/STi hardware? If I recall correctly, the word was that KYB licenses some of the technology used in the STi strut design from Bilstein. Also, didn't DMS blame some of the problems they had with their DMS Gold 40mm struts on bad guides they sourced from Bilstein? The guide for the strut cartridge in an inverted strut is very important and is a likely culprit in clunking and sticking STi struts. Lastly, didn't Prodrive WR (Bilstein sourced struts) suspension owners complain of a bouncy ride as well?
With regard to Ohlins fixed perch struts, they do have a significant design difference, an internal reservoir. There is a fixed plate, with valving, between the floating piston and strut piston which forms the "internal reservoir". The valving in that fixed plate performs a similar function as that of the valving on a remote reservoir or the foot valve of a twin tube strut. With the early reports being all positive on the Ohlins, I'd be curious as to what other design differences there are over the STi units? Better guide design? Beefier piston shaft?
If it is a new design that is being sought after, why does everyone seem so set on inverted struts? Has anyone ever done the math on the bending stiffness of the STi inverted strut cartridge vs the WRX's very beefy strut shaft? What what be the resultant camber change for a given lateral load due to the bending? Are we talking here, a .1, .2, .3 degree difference when pulling .80, .85, .90 Gs? Of course, this would be assuming the guide could keep the strut cartridge straight relative to the lower housing. Which by evidence of recent pictures, it can't. Correct me if I'm wrong, but don't many of those European cars use McPhereson strut set-ups up front with non-inverted struts? If that's the performance and ride quality being sought after, then why the insistance on inverted struts?