Agreed that they are cool models. However, I think that the uncertainty is the problem. Most chaos guys are good when they are specialised and meant to kill one thing. You know pms will survive on the objectives, you know that a khorne lord will charge, you know that termies will deepstrike and kill tanks/ics, and you know what chosen are geared for.
The real problem with possessed is that they are elites and around them are Chosen (whom you can gear for pretty much anything) and termies (same) so why would you choose possessed over either of the first two elites? I really do agree that they are cool models, but look at their points cost. For 300ish points (10 guys and icon) you don't know what they are going to do. With 300 points that's around 6-7 kitted out termies.
I almost said that's about 10 chosen too, but you wouldn't even spend 300 for a good squad of chosen because they're so cheap, even with power ups.
I like this article, but I'd never use possessed in a tourney.