Well,we all know how the sharingan has three forms.
Sharingan>Mangekyo Sharingan>Eternal Mangekyo Sharingan.Each form is reached kwa doing progessively darker things,but i'll get to that later.

First,the color schemes.The sharingan is Black and red.The byakugan is white.Black and red is usually a color pattern associated with demonic stuff,right?So,in theory,The Sharingan is the Demon Eye.The white of the Byakugan is the complete opposite,as white represents purity,divine quality.Hence the Byakugan,the Angel Eye.What does this have to do witha possible evolution?Well,i'll explain.

Unlocking the Mangekyo Sharingan requires wewe kill your best friend.This,in my eyes,is a step towards the darkness,because wewe are severing the ties that connect wewe to people.the ties that make wewe human.Then,in order to obtain Eternal Mangekyo,you have to take the eyes of another Uchiha and implant them.This is also fairly inhumane,and a bigger step into darkness.In this way,the Sharingan requires embracing your darkness.

The Byakugan,representing the Lighter side,would have a different way to evolve.Instead of embracing your inner darkness,you'd have to defeat it,and remove itfrom your spirit,Making wewe basically pure.So instead of stepping into darkness,you'd step into light.You would then achieve a pure version,an evolved form on the Angel eye in my theory,The byakugan.I know that Sharingan and Byakugan don't really mean Angel and demon,but they fit my theory.Whaddya think?