Each of the 4 Chaos Gods is unique, with fairly clearly defined portofolios. The Horned Rat is 2 parts Nurgle to 1 part Tzeentch. While it may be a power in it's own right, it's not a replacement for Slaanesh. For that matter, the Chaos Gods are jealous of their own power, and probably the only thing prevent Nurgle and Tzeentch from teaming up to layeth the smackdown on the new guy is the fact they hate each other more than they do him.
Maybe this is part of some exciting campaign plot line. If so, I can grudgingly accept that.
If this is just GW trying to pander to the kiddy audience, then no. I started with the Realms of Chaos, that were recommended for mature readers.
I don't play Slaanesh. I'm not particularly interested in Slaanesh. But I will not accept Slaanesh being written out of the lore the same way the Squats were.
I agree pretty much line for line. Then again, I really am not really thrilled with -any- of the new fluff so far. It feels so overly generic, as if it was written by a 12 year old.
From what I've seen, the whole Slaanesh disappearance -sounds- like it's a precursor to either his/her/its removal, OR some sort of massive re-design. There are literally countless predictions on various sites, but there has been the confirmed disappearance, and the confirmed ascendancy of the Horned Rat.
Like you, I am hoping that, at the very least, this is part of some sort of 'big campaign'. Without points-costs and whatnot, supposedly the focus is on scenario play, and as such, having some huge amount of campaign-based scenarios focusing on the 'return of Slaanesh' could be good. Time will tell.
And no, even though I dislike Chaos and have from the very beginning, I do -not- want to see any of the big four 'written off' like Squats, Zoats, Fimir, etc. -Especially- if it's for PC reasons, when the game lines GW sells deal with -mass slaughter- of epic proportions on a daily basis.
My interest is pretty high - I've been active with each edition since 3rd, but I am definitely going into it with an open mind. I have enjoyed the handful of games I've played so far, but me and my buds are very reasonable when it comes to force construction, and we create our own objectives, etc. Playing the game straight out the box, as presented, is very... lacking, in our opinion so far. But the coming months will be telling.