By 2015, Jaguar will have an all new BMW 3-Series Rival ready. Along with the 3-series it will compete with the Lexus IS, Cadillac ATS and other small performance sedans. Chances are it might used the same V6 and V8 engines the new F-Type has, along with smaller engines such a N/A 4 cylinder, 4 cylinder turbo & maybe a hybrid powertrain.
Due to CAFE fuel economy standards I don't think the V8 will make it since with something as compact as this they'll try to push the whole fuel efficient thing on it. If the V8 does make it, I have a feeling it wont be till years after the XS launches. Still can't wait for a Jaguar XS-Type V8 S