Every few months, I would love for them to rotate in new 3* prizes from the 2* champion rewards. I have a few 3*s getting lots of champion love, like Hulk or Cap Marv, and lots that don’t get any love, such as IF, Doc Oc, I think.. I don’t remember, but you get the point.
Anyway it would be nice to rotate to so that they all got some champion reward love at some point.
Interesting point. 2*s champ so fast there would hardly be anyone ‘missing out’ on anything. Only thing I can think would be newer players who are on their first run through and actually actively using the covers as a non-random way to progress. For them it might be hard.
Alternately, maybe every time you champion a 2* for not the first time the champ reward covers are for a random 3*. Doesn’t even have to be the same character for the 3 covers at that point. That way new players get 3 covers for a known 3* character that they can focus on, and everyone else gets something new 
I wonder, though, if it’s “better” to have ~10 or so 3*s with higher champ levels due to this, or if it would be “better” in the long run to have a (presumably) more even distribution.
That depends on the 3* you are talking about. Having a huge 3* hulk is more a liability than anything else. The bigger he gets the less likely it is that Anger procs… so sad.
This is a valid point, however. There are 42x 3s now, and still only 14x 2s. I’m not awesome at math, but the calculator app tells me that means there are 3 times as many 3s as 2s. You could also, at this point, have a fixed rotation of 3x characters linked to every 2*. Or you could give 1 cover each for 3 different heroes on the path for every 2*.
I like the idea of randomly assigning a linked character and it is fixed when you push the promote button. But that’s the opinion of someone who has lots of champed things.
I also like the idea of offering the player the option to select from a short list of options when they click the promote button. The same could be done at the 3*->4* link. Let people pick from one of 3-5x 3s for their 2 champ to award, give them a similar set of options for the 3* promote button.
I think the most important item here is that the link needs to stay, or players should be able to decide if they want to have the linked character changed when the connections update. I know a few people who were disappointed when the links were revised a few seasons ago - and a cover they were looking forward to getting as a champ reward had shifted to another character.
If 2-stars gave 3-stars the whales would know bliss.