They've already made it hard enough to make sure legit email ends up in the inbox of a gmail-recipient, rather than being silently flagged as spam -- that anyone hosting their own mail needs to consider if they need to special-case delivery for gmail recipients (I've considered routing gmail-destinations through authenticated smtp to gmail via a gmail-account - then realized that that was just silly and I feel better when gmail doesn't work -- but I don't depend on delivering my (private) email for revenue). Add to that the fact that google is one of few big email providers that are hard to grey-list (or rather automatically white-list once delivery has started) -- and they've already made a great effort of siloing off one of their arguably most open services.

If you think the megacorp that doesn't do customer support is going to be any easier to dislodge at other levels in the stack, once they manage to squeeze themselves in by undercutting the market, I'm afraid you're hopelessly naive.