Well with more details being "confirmed" about the Grey Knights codex it feels like they might be the rules match I am looking for in my Thousand Sons. I still plan on waiting to have the book in my hands before I commit to even buying more models. One unit I WILL have is a maxed out unit of terminators. It looks like only minor conversions will be needed to make them fall into the heresy era look that I want.
Power armored troops will still be MOSTLY forgeworld Mark 3 and 4, but the gear is all custom either way. I am really looking forward to this book. I feel like this book will be a real high-wire act between numbers and quality of forces fielded. I look at this as a challenge, but also a HUGE opportunity for modeling.