I always am curious when I see this. I've planned and deployed master setups in two separate 10^4 node count companies now. In my experience the number of hosts doesn't really matter (figuring out an architecture that will work with availability zones etc only takes a couple weeks). The real work is figuring out how to normalize and govern the repos. I haven't seen any sane ansible repo once it's beyond a few senior contributors because it's so easy to do whatever you want. Ansible is the ultimate small business tool, but it works very poorly in large companies.