As an
I'd say no. She doesn't need any changes (as of right now at least. We don't know how pre-season will effect her yet). She may be out dated when compared to others but she is in a good state with her play/win rates and counterplay so she really doesn't need a rework.
Also your changes would kill
as a champion and part of her theme. While it is true that her current passive won't save her all the time...you just got to know how to play around it and the egg is a huge part of what makes Anivia what she is, a Phoenix. But let's go over how I feel about your changes...
Your new passive idea wouldn't really work out to well, considering that you would have to use basically your entire skill rotation to get a target to the 4 stacks (unless you could keep target in your ult) and even then you really wouldn't have the skills to be able to proc it. Now if you made the chill stack on Abilities AND Auto attacks, then that would be more obtainable for Anivia. Because the way you have it, your Q would give 1 (or 2 if her Q still procs damage twice), E would be 1 and then you'd need the other 1-2 from your ultimate. There is to much delay and counterplay in it that would make it really hard for Anivia to ever get her E off with full stacks, at least in a 1v1.
Your Q seems to be about the same or so. Looks like your changes to that was reducing the size of her Q projectile but making it faster which is a fair trade off. Your W seems to also be about the same but for freezing people near it if they had 4 chill stacks, which tbh is a bit much because her Wall is actually pretty OP right now already and is probably one of the main things people complain about her.
I don't like the idea on her E. You really buffed up the damage on her E since her base E would do 60% AP and then up to 80% more based on chill stacks, and I think 140% AP ratio on an ability that could potentially be point and click is a bit much. It becomes even stronger then other champions ultimate. Though you do make it much harder to pull off, where it requires your entire kit now but that is also another reason why I don't like it...It'll be almost impossible to really hit an E on some one with 4 stacks of chill when your ultimate is on CD which you put a large CD on it.
Your ultimate suggestions: This is the biggest problem I have with your rework and why I feel it'll kill Anivia. First of all you are basically removing her from being the queen of waveclear and stalling and making her a terrible to mid level wave clear champion with the changes to her ultimate. Putting a 2 minute CD on it means that it's no longer usable to wave clear with which means your entire wave clear is based on your Q...which is actually really bad at waveclearing.
Also it can be hard enough in some match ups to even get people to go into your ultimate when you are facing mobile champions. At least with Anivia now, if they run out of your ultimate then just deactivate it and try again in like 7 seconds but with your rework if they get out of your ultimate...you are out of your ultimate for 2 Mins and your chances at even getting some one to max chill stacks dropped.
It would basically feel like a new champion and people hate those kinds of reworks when a champion is changed so much that it doesn't even feel like you are playing them (Unless it was necessary because the old style of that champion was to toxic or op like old
).
tldr: No, your suggestions would remove her from what she is which is a phoenix and would kill everything that is good about Anivia like her wave clear and her team fighting/zone control. She doesn't even need any changes at all and is in a good spot right now anyways. Yes she is an old champion and some things might need updated, but nothing like a rework imo.