Could Necron be next tier boss? My thoughts and yours?

[Hasrat]

Can't imagine why it would. Necron kinda came out of nowhere, and I don't think was very well received by fans of the game.

[Kyuuen]

Necron kinda came out of nowhere,

As a fan of IX myself, I really hate this statement. Kuja was trying to destroy the crystal to bring about nothingness, to return everything and all existence to zero. Clearly he failed at that, seeing as the story had a conclusion with the characters. However, his attack had enough of an effect to; arguably, bring all those in Memoria into the Zero realm. Necron was most likely a guardian/deity/god of that realm or in the very least one of the inhabitants who grew strong.

I will admit though, that due to the lack of information regarding anything like the Zero realm it seemingly comes out of no where, but at the same time it's not exactly too hard to explain either.

I don't think was very well received by fans of the game.

It had mixed reviews due to it being overshadowed by the PS2 release and; in my opinion, FFX's advertising also probably had some affect. But in recent years it's gotten more positive light.