While it is impossible to create a world of perfect equals, it IS possible to create a world that is more equitable. You could create education for commoners and allow them to be allowed to show off their talents and pursue goals, raising them up. Commoners will inevitably begin to gain more power as a result of the more talented individuals being able to live better lives as a result.
The more commoners that become educated, the more free thinkers there will be, and the nobles will inevitably lose their power more and more. No matter how much nobles try to oppose it, once you give commoners education, it cannot ever be taken away.