He's the rightful king if the Targaryen line takes the throne again which is going to lead to conflict with Dany since his existence invalidates her claim. Jon will likely have to go to war as a means of defence as Dany will reluctantly have to fight for her right to rule. I think it's going to be the main conflict in Season 7 which would be interesting since it would be different to the wars in previous seasons since there wouldn't likely be a clear cut villain and hero as it would be a war of circumstance and necessity. Neither side want to hurt the other but only one of them can survive.