Well more or less your opinions on the ruleset are pretty moot. You'd stomach any and anything just to play your sisters because, as you said, you just like the models. I'd like to say this but I also see 40k as a game (because it is). It is both a hobby and a game. Thus, as a game, I prefer to not gimp myself for the sake of liking something and to this degree I'd like to play my sisters...but I also don't want to play my sisters. Rules-wise there is nothing spectacular about it. I personally feel the new faith, as a mechanic, really strips out the heart of the "feel". Its boring and fairly unoriginal and leaves faith powers in the seat of "oh they felt better so they did it" rather than actual forces of change.
They might stay as an "unserious" army but be shelved at the point when any real competition comes around.
All the world will be your enemy, Prince of a Thousand enemies...Be cunning, and full of tricks, and your people will never be destroyed.