This is a really interesting question and I'll get Liam and John in to answer it properly. Matt has actually become really good at producing high-quality models, textures and animations with relative speed but that's only a part of it. Also for a new species there will be multiple models and animations needed (worker, specialist unit, melee soldier, queen in most cases).
Once early access is out and the guys have had a short rest I'll ask them to come and answer this question fully because it's a great one.