>the most desirable option would be a reliably "benevolent" mega-corp that could be trusted to prioritize the user experience while also horizontally integrating across product segments to create a unified service.

Why is that desirable? Its not to me. The most desirable outcome is open data exchange standards that allow data exchange so that ANYONE can build such a service.

Google locks-up publicly available data and they subsidize/price dump to offer services at no-cost so other players die out leaving them to manipulate the market as they see fit. Its the worst possible outcome for everyone involved.