I think it would be enjoyable to be able to adjust your spring rate at the touch of a button instead of swapping out springs. And I'm really planning on getting front air bags, but I was thinking also about rear bags to add onto the leaf springs. But I wasn't sure with rear bags, but I'm totally gun-ho for front bags.
New age air bag systems have much to offer. I just read about a system for a WRX. The car's lap times were a tic off a full race coil over set-up! It was an adjustable set-up. Stock height/lowered/track. The "spring" rates went up and it adjusted the alingment to suit. I think you may see that air bag systems will become more popular in the future for performance cars.
I have a Mark 7 which has stock air suspension. I have a love/hate relationship with that system. The car handels well, but the seat of the pants feel is a little scary!
Air bags on a SLA (Short/Long Arm) front suspension are a bad idea, just like air shocks on the front. Reason being that the camber changes dramatically as the arms move up and down.
The Mark VII gets away with it because it's a strut suspension, and the strut by way of being bolted to the steering knuckle (spindle) holds the camber to a tighter range of motion.
The difference being that as the two steering axis points move (they move in/out as they move up/down) on a II, they are at different arcs, versus only the lower point moves on a strut-type suspension.
A few thoughts/ observations/ speculations ....
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First, you can't change the spring rate with the touch of a button, you can only raise or lower the car. <explanation follows>
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The amount of "wallowing in hte corners" will depend on the type of bag used.
There is the style of air sack that is really nothing but a bag of air, the greater the load the more it compresses and the spring rate is somewhat lineal.
Then there is the type of sack that has a "conical" end (more parabolic). The more weight/ force applied collapses the sack moving the cone into the bag reducing the volume and effectively increasing the spring rate.
I bet one could go through lots of money buying bags of different diameter and length with different cone configurations before finding one that suits them just right.
A bag that was 'perfect' on my V6 car probably wouldn't cut it in my Windsor car.
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The range of motion things a good point. But if both ends of the sack are on pivots that will allow them to pivot and self align thus staying somewhat paralell this isn't / wouldn't be a concern. Believe me, bags under pressure want to align themselves.
There is a certain amount of swing bags with fixed ends will tolerate. I think the front of a II would excede this tolerance.
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I wonder how much of the wallowing in corners are due to the air bags supply lines being 'T"ed together instead of being valved seperately. ? Even if the 'perfect' bag is used it can still wallow like a SOB. Go into a corner and the outside bag collapses thus increasing pressure which is transmitted through the line to the bag on the corners inside which tends to extend it. YeeHaw! Just imagine an exit ramp ...... will it ever stop rolling to the outside???
Each bag needs it's own valving.
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You can't use the shock mount points for an airbag without reinforcing the hell out of the mounting points. Shock mounts are designed to absorb forces from dampening suspension movement, their not designed to support a load. This is the problem with air shocks. In days of old it wasn't unheard of to have air shock tops protruding into the trunk.
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An air bag and a shock absorber can't share the same space unless the bag has a hollow center. I have never heard of a bag with a hollow center. There would need to be an alternate layout for the shock.
I remember reading in some car magazine a few years ago (Hot Rod?) that was going in rides in a bunch of cars with air-bag suspension and interviewing the owners on whether they like them, the pros and cons, etc.
I don't remember much, but the one thing that stuck out in my mind was that they finished saying that the air-bag set-ups that were designed and manufactured by companies were great (if that is the kind of suspension you are looking for) but if you have to fab your own don't bother because they usually end up like crap and your bouncing all over the road and there is lots of roll.
Of course you could look at that and say that it just another magazine trying to sell its advertiser and stick it to the man, or you could look at it as society created engineers and specialists for a reason.
Looking in the street rod magazines, several companies seemed to have an airbag setup for the II. But I think they required a different crossmember design with a custom "spring hat". And these would generally be designed for cruise and show work and not for serious road or track use.
Some of the coil-over setups seemed to offer some of the qualities that you are looking for...i.e. "relatively" easy-to-change spring rates and ride heights.
Ok, so I have thought of air spring before. I havent gotten around to doing the measuring and math.
The first thing I'm thinking of air springing is a trailer. I figured it would be trick to have a trailer where I can dump pressure to the springs to lower it for loading the L/G tractor or motorcycle.
Get some experience on a trailer and move onto a car.
BTW, I would take the advice of a Specalist Technician over that of a Engineer.
It's about the best one I've seen. You obviously have to run their upper and lower arms to be used with it. Give them a call if you have questions, they are very helpfull on the phone. I got my brake kit from them.