I don't think a Cadillac sedan off of Kappa would be a good idea - Cadillac definitely should stay up market, and not make the mistake of chasing too far down the totem poll like M-B has done w/ their C-Class Hatch, or BMW is doing with the coming 1-series.
But, a Cadillac roadster, priced in the $35-42k or so range off of Kappa could be pretty cool. They could use the extra $ to of course beef up the engine, perhaps add something like magnetic suspension, improve comfort and ride quality, and offer a world-class interior. Assuming it drove as well as a Z4, they could easily sell a lot of them if the styling was right.
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Thanks for building it Bob!