They would have captured 100% of the messaging market. Reminds me of '90s *Nix companies with sales bros wanting to sling around overpriced hardware, preventing expansion of the company in other fronts.
But I'm in the US, which has a disproportionately high amount of iOS users. Across the rest of the world iMessage would be competing with WhatsApp and its existing network (something the e-mails in the article note) and I think it would have been an uphill struggle.