I'm pretty sure you wanted to say 'stuck on 14nm for most chips'.The performance will be interesting to see. Intel has been stagnant for years, and still stuck on 10nm for most chips. TSMC is building 5nm chips for Apple.
As for the transition, the PPC to Intel transition went very smoothly. I see no reason why this won't also go smoothly. Although its a bit comical that Apple has gone from CISC (68k), to RISC (PPC), to CISC (Intel), and now back to RISC (ARM).