Although the F-Duct is banned for next year, it hasn't been uninvented. Ever since its ban was confirmed, you can be sure that scores of Formula 1 aerodynamicists have been tasked with coming up with a fluid switch to achieve an aero advantage, even if it doesn't any longer play upon the rear wing.
Similarly, although we're theoretically back to single-deck diffusers next year, just how certain can we be that some other fiendishly clever way will not be found to replicate the effect? Judging by Ferrari president Luca di Montezemolo's recent comments regarding his fears about how the new moveable-wing regulations might be interpreted, there is an underlying nervousness.
McLaren engineering chief Paddy Lowe describes the dread he feels awaiting the launch of new cars from rival teams: "The big worry is always to see whether anyone has found a trick we've missed. Is there some angle we haven't thought of, some trick with suspension layouts or whatever?" It seems everyone is feeling it particularly keenly in anticipation of 2011.
Ruling the twin-diffuser interpretation as permissible in 2009 arguably made that season, in that it left usual big-hitters McLaren and Ferrari desperately trying to claw back an initial disadvantage to Brawn. But that wasn't the whole story.
In readiness for the double diffuser being banned, Brawn had a single-diffuser version that the tunnel said was just a few tenths slower. It would still have been significantly faster than a good conventional car like the Ferrari (though would almost certainly have been eclipsed by the Red Bull, which even in original single-diffuser form was almost as quick as the twin-diffuser Brawn, and significantly quicker than the twin-diffuser Toyota and Williams).
The point is that the concept of the twin diffuser led the Brawn design team along a certain aerodynamic path - the concept of the front wing, the profile of the nose and sidepods - that proved fruitful regardless.
This illustrates a law that invariably applies in racing: the genie will not go back into the bottle once released. So might the fluid-switch principle that made the F-Duct work be directed instead to stalling the airflow to the radiators at high speed to reduce drag, for example?
McLaren F-duct © Sutton
The idea of active aerodynamics that physically moved a more aero-friendly surface ahead of radiators at high speed has already been discussed as the basis for future permissible technology. But this would obviate that by achieving the same effect via the fluid switch.
How easy would that be to accomplish? The fluid-switch principle - whereby the airflow is suddenly diverted in a completely different direction according to pressure - could potentially be used anywhere on the car, and need not necessarily involve the driver blocking/unblocking a hole within the cockpit. Could there be a way of advantageously using the principle in conjunction with the moveable rear wing?
Similarly, the effect of the double diffuser could be replicated by having other parts of the rear bodywork diverting air to the appropriate place, so that it scavenges the flow from the conventional diffuser ramp much more powerfully.
The key to this would be in feeding these other bodywork shapes with a flow introduced from the floor when the previous loophole - that the transition from reference plane to step plane was not a transition, but two separate surfaces that could therefore have a gap between them - has been closed. But does that necessarily mean there is no way of getting flow through there? In this age of carbon with non-linear load deflections, might there not be some cunning way of getting around this without actually breaking the letter of the rules?
If there is, someone will figure it, it will be on their car and then the controversy kicks off. Round and round on the hamster wheel of F1.