Despite all this my preference is for a grot soup tome that includes all goblin models, like what Death got. The idea of painting 200 goblins for a new faction does not appeal to me.
But as for rumours, all I can share is that I chatted with some staff at warhammer world, trying to tease info out of them about the new grot tome, and their body language and faces basically confirmed it's incoming. (I'm probably reading too much into this)