Well yes, granted the last two perhaps, though I don't see the A320 family getting re-engined for a second time.
But putting new powerplants on 5-10 year old designs hardly qualifies as "grandfathering" when compared to certificating 4 distinct generations of an aircraft over a 50-year period on the same TC.
What I can see though, is putting the wings from the C-Series -500 on the A320, or a further design of that wing. A metal tube, composite wings with new engines, this would be a formidible design for at least 10 years. After all, it would be up against the MAX series, which I think has been flogged enough.
Boeings clean sheet FSA (future small aircraft) single isle was not due until 2030...and the E series, is well, virtually dead.
Boeing brilliant concept to knee jerk the NMA, a 767 fuselage with composite wings....really?