Why would Toyota wish to dilute their dominant position over GM with one of GM's biggest turkeys. 
Three reasons: Audi A3, Mercedes B-Class, BMW 1-Series. The luxury hatchback scene is taking off, and Lexus (1) has no credible entry, and (2) has no name credibility with people who like agile, sporty cars (I'm not dissing their incredibly posh sedans and SUVs, though). Lexus doesn't even have a sporty crossover like the RDX and FX. If they want a credible entry into that expanding market, they're going to have to think of something creative.
GM killed Saab by forgetting its past. They don't even SELL a hatchback besides the rebadged Impreza. Instead, they've got midsize sedan/wagon, a large sedan/wagon, and an SUV. I see Toyota as doing something very different with Saab. Saab could be to Lexus what Scion is to Toyota--just a couple of models with more spunk but a bit less refinement, sold under a different name out of the same dealerships.
If I was Toyota, I would buy Saab, and end their entire current model line. I would then use a single, sporty FWD platform (maybe even derived from the last-generation Celica). I would take one of my reliable four-cylinder engines and turbocharge it. I would then make a three-door hatch, a five-door hatch, and perhaps a convertible that all had the unmistakeable silhouette and interior oddities of the older Saabs. It would have more sport and less luxury than your typical Lexus, and would be priced to compete with cars like the A3 and TSX.
If that sort of car was built with a Lexus name, I think it might (1) lack credibility with the target market, and (2) "dilute" the Lexus name by introducing a four-cylinder and a car cheaper than their current offerings. Two serious negatives. If that car was sold under the Sasab name out of Lexus dealerships, I don't think either negative would occur.
Oh yeah--and I'd come up with a better ad campaign than that "born from jets" c---.
I honestly think that that could resurrect the SAAB name from what GM has done to it.
