I think J-XX will make its maiden flight around 2020. That's my best guess.
A cheaper next generation aircraft along side the more expensive and technological consuming one would be a very low RCS Chinese flanker, with engine placement alterations and air inlets.
For single engine aircraft the engine must be extremely reliable and fast start up time. China turbofan sector doesnt have that kind of reliability yet to install domestic engines for single engine fighters its currently most advance turbofan WS-10A has a slower start up time than its Russian counterparts.
For double engine fighters (eg. J-11) the WS-10A will do fine but for single engine aircraft (eg.J10) it isnt up to scratch.
If China wont allow WS-10A to be fitted into J-10 due to reliability issues they sure as hell wouldn't install them on their most advance fighter jet.
Current PLAAF is pretty sufficient my thought would for J-XX is that its aspect is the same as F-22 but its secondary role is for nuclear strike missions. A Fighter-Bomber stealth aircraft with agility like fighter aircraft and stealth as a stealth bomber.
J-11 RCS reduced from 25+ to 5 which is a substantial amount no reason why the J-10 cannot also reduce its RCS