Did someone say "meow"? Sorry couldn't help myself. I've run across this online too but I just don't know about pretending to be a cat. I know they're are like some totally fanatical cat lovers out there that might be super into this.
Well if you have read the books and like the story and characters (93% of which are cats), it's not at all difficult to pretend to be a cat, you don't even have to be a great cat lover, I prefer dog actually, and I love the series.
I'm not part of this but I thought there was already a major community for this that's pretty active why do you want another one?
I can't post links here I just looked it up and found some other sites that made RPs about it. Maybe those are the ones you said fell flat. I didn't look at it in depth, like I said not into this.
There is a free (I think) tabletop roleplaying game called CAT (or CATS?) where you do roleplay a cat, but a normal one, mostly, I think you help keep goblins from hurting your humans or something, it's been a while. But I presume you're going the anthro route with this.