That doesn't imply that. Mazda has introduced engine upgrades in the past that don't coincide with the gen change. Mazda has already said that the Mazda6 will be getting the Diesel soon after the CX-5 so there will be 2 engine option with the 4th gen.
Skyactiv is not just an engine upgrade. It's the brand name for a range of technologies:
SkyActiv 1 wasn't dribbled out to old body styles. It coincided with an overhaul of the entire Mazda line. If SkyActiv 2 is a significant step change (which it's purported to be), I just don't see them dribbling the tech out as incremental updates to the gen 3 bodies...or substantially revamping to Gen 4 bodies built on the SkActiv 1 platform for one year, and then slipstreaming SkyActiv 2 a model year later.