He basically wanted to become YA
He already accepts that. He just doesnt have any hope of anything better being possible. He's basically praying that we succeed while keeping the bulk of himself ready incase we dont.You know, R'hllor's overarching plan isn't dissimilar to our own. It is, arguably, one and the same. Turn all the cosmos into a dichotomous battleground of Light against Dark. Of course R'hllor would have the head this confrontation in the side of Light... he was brought into being as a god, his nature forbids him from playing any other part. Viserys can only bring together and unify so many disparate and distinct powers under one cause because he has the freedom and perspective of mortality.
Ultimately, our goal is to turn the final battle into one of light against dark. Only a lower case 'light.' Rather than all being bound to a single entity, all the factions of the world will bind themselves to a single cause. Not necessarily a perpetually unified future, merely the concept of a future.
R'hllor all but admitted we are the closest thing to his chosen one. Maybe we can convince him that are causes are actually the same thing, just seen from different perspectives?