A Speed CX3 would be incredible.
After a lot of thought driving my CX3 I've come to the conclusion that a Speed CX3 would be amazing. First off, let me say, I owned a 2011 Mazda3. My girlfriend currently drives a 2014 Mazda3. The CX3 really struggles off the line for me. It feels very anemic until it either goes to second gear or gets up to 4000RPM. I miss the much better off the line grunt the Mazda3 has. The CX3 really needs more power, the 2.5L Turbo they put in the CX9 would be right at home on the CX3.
A CX3 lowered 2-3 inches with stiffer suspension, better tires, bigger engine, and a 6-speed manual would be a contender for the best hot hatch available in the US. (Supposing you could call the CX3 a hot hatch.)