In reply to Marcus Tibesar.

Hi Marcus,

I am quoting from RankMath's official reply here to the same question.
​
"​We do plan on releasing a paid version but that will have additional features. The free version will always remain free with all the features you see in the plugin right now.
​
​You can check our roadmap for more details: https://rankmath.com/roadmap/
​
​Hope that helps"