Such a person would need a variety of skills, talents, marketing, luck and hard work. The best situation would be if they were multi-talented and extremely dedicated to creating and selling their work based on MLP. I'm talking, art comissions, advertised music, fan made merchandise, YouTube analysis and more. All of which done consistently and with high quality enough to make them very popular. With these conditions met I believe a career could be made from MLP independently.
But then you have to deal with Hasbro's cronies.