I am leaning towards that way myself. But like you say, you need to work out exactly how it works. As it stands, SM models every bullet, so Suppressive Fire as written (with a minimum of 5 /10 and no maximum) has some abstraction in it.
I think the ruling I've been working on (as it doesn't come up very often) is that a burst does AE * number of shots (i.e. 3, 5 or 10). For Tracking Short/Spread Burst/Aimed Burst Continuous Fire - which only applies to a single target - this works okay.
Like you say, it's when multiple targets come in that the disconnect comes in, because Suppressive Fire turns it into an area-effect attack and you're not modelling every bullet/shot anymore.
So. I reckon putting some more limitations on that is in order.
Maybe say, then, that you can only make (effective) Suppressive Fire on a maximum number of targets equal to one per two bullets/shots fired. You would then let people pick how many targets they are trying to suppress (with the proviso that targets must be contiguous).
You'd work on the basis that if you're not dodging or taking cover from the fire, what shots would normally just be in the vicinity and not have any real chance of hitting the target proper ('cos they are really there to keep their heads down) will hit and degrade the shield.
So then say that the AE "on target" as far as shields are concerned, is equal to AE of weapon (x 2 if continuous weapon) plus number of bullets/shots divided by number of targets. (So if you spray, say eight targets with auto fire, you'd need for fire at least 16 bullets (and effective AE would be weapon AE+2). But you could say, fire 64 and effective AE would be (weapon AE +8).
If you concentrated one just one dude though, you could suppress that one target with 64 bullets and get (AE +64) to shields. (Which will be more than you can do with most continuous weapons with an aimed burst.)
The actual attack resolution would be left unchanged (since there comes a point where, it terms of hurting people, it doesn't really matter - you'e not really aiming at them, just putting lots of fire in their vicinity). If you're shooting a horde of unshielded mooks, it works no different to normal, so you suppress as many as you can. But if you run into shielded targets, there's a benefit to concentrating your fire.
So then it still behooves a shielded target to take cover from Suppressive Fire, since while their shields mean they are unlikely to take any (more) damage from a Suppressive salvo, the concentration of fire of lots of shots pinging off your shield will mean it won't be UP for very long.
(You'd say, I guess, if you do take cover, you only count the AE as being for one bullet/shot.)
Yes? No?
Edit: I talked to some military experts of my acquaintance, they concurred that the manuals say that one bullet landing within about four feet is what they reckon is enough to make people duck, so the estimate of one target/ 2 bullets/shots is a plausible order of magnitude abtraction.