One thing Lossie does have is space and this will be the reason it was kept versus Leuchars, despite the latter having famously been renovated to support another 40yrs of fighter ops!
Re-opening Kinloss (for 9 a/c) is a pipe dream in my opinion, but agree that basing P-8 at Waddington makes some sense. What would maybe have more sense would have been to establish a 3rd Typhoon MOB at somewhere roughly inbetween the two current bases. Leeming? Leuchars? But I'd imagine budget constraints put paid to ideas such as those.