I really like the Idea of Nunu Buffing AP champions but...
Why was he the only one changed that way? Everyone will call him op and his statistic will rise up because he just brings a new Meta to the table. Just like what you did to Mordekaiser. You tried to bring a new Meta to the table but you only brought 1 champion into it. You need to change a bunch of champion if you want to bring something new to the table or else Nunu will get nerf just because he breaks the current Meta.
Transitioning from the current Meta to a whole new Meta can be done quick if you guys just bring more champions with unique feature into it. Like Making Janna E give AP, Lulu Shield give adaptive CDR or attack speed depending on the champion.