Well if they take Kimi they have to change the perception that it's Vettel's team, is my point. We can all see that Vettel is better than Webber, but I don't think that'll be the case with Kimi, so fans won't accept bias.
To me both Sebi and Red Bull Racing are amazingly unpopular, considering what they've achieved, and to some extent those two are linked I feel. RBR can fix some of that with Kimi, IF they don't blow it.
Though if it were up to me I'd replace Vettel with Kimi, job done - win on Sunday, sell on Monday.
My general impression is, Kimi really is well-liked. He has nowhere as many haters as Vettel/Alonso do. But the thing is, popularity is a relative thing. Vettel/Alonso are easily the most popular drivers out there in the sense that everyone and their cat has heard of them. The two of them are the ones fighting for WDC in the last few years and they are also the most titled. Even if they are hated by many, their names are well-known. Vettel is a brand, like it or not. Same goes for Alonso.
Why do even the most casual F1 fans (even those who hate Ferrari/Alonso/Vettel--or especially those who hate them), want to see FA and SV in one team? Not Kimi&Alonso, not Kimi&Lewis, and not FA&LH (we've seen that already), but Alonso and Vettel. Because it'a thrill, because it's exciting, because FA and SV both have their share of haters who want one of them to be destroyed by the other --and at last, because some drama is guaranteed. F1 is a show. A show needs drama and villains. It makes a good story.
I agree with you that Kimi would be great for Red Bull to sell RB. Vettel would be great for established teams like Ferrari and McLaren. If Vettel becomes a Ferrari driver, his negative popularity would convert into a positive one. He's so disliked because he keeps winning against the established stars of established teams.
Just my opinion. I don't claim to be right, but that's what I think.