Given a site which is not optimized for mobile (and not responsive), Google's new ranking algorithm, which is set to go into effect April 21, 2015, will result in a lower ranking.
If the site does not currently have an "m dot" site (m.example.com), would introducing a new site at the new domain solve the SEO problem? Or would it cause another one? Wouldn't that the pages to be indexed twice?
Responsive design is clearly the best solution for maintainability and certainly solves the "mobile-friendliness" problem, but I'm curious if introducing a mobile-only site would also solve the problem.