I kinda like the high number, as it means the spirit is to prevent monopolies, which is one of the most compelling reasons for regulations to exist. Make the number too low, and it would invite criticism from people about regulations being overbearing. I don't know if that number is 100M, 10M, or 1M, but just something to be mindful about.
My sense is that if Facebook is legally forced to interop, then all other smaller/future players will voluntarily interop anyway.