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The reason that downforce works so well in improving handling is that the downwards push on the tyre increases (so increasing grip) but the mass of the car doesn't change. Therefore we have more grip without having an increased mass to accelerate (forwards, backwards or sideways).
Now contrast that with lift. Now we have less downwards push on the tyres, so decreasing grip (and, as the diagram above shows, sometimes disproportionately decreasing grip) but we have the same mass to accelerate (forwards, backwards or sideways).
Furthermore, the current research evidence (see my book pages 180 - 182) shows that lift, even small amounts of aerodynamic lift, has a major effect on car stability. (We're talking a couple of kg having a measurable affect.) That may be because the aerodynamic forces are oscillatory, and therefore may resonate with unsprung weight and/or suspension natural frequencies. Either way, all the evidence is that any aero lift reduces stability, handling and braking.
I therefore don't think that makes sense in cars on public roads, even with sensing systems and electronic over-rides. But it's easy enough to prove for yourself. Just put some high lift wings on your car and assess control and stability versus improved fuel mileage.
Going the other way (ie from lift to downforce) with my road car was an enormous learning experience, one I notice each time I drive my wife's Mercedes that has quite a lot of rear lift (maybe 10 per cent?).
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