I don't think Majestic should be an Earth-based hero any more. It presents a couple significant problems. For one, his methods don't mesh with modern superheroics in the DCnU and his attitude might make him somewhat of an antihero when he's showcased next to some of the paragons of virtue that make up the face of the DCnU. I admit though, this may not be as huge a concern as it would have been in the DCU. It seems as though the heroes are less perfect and, shown especially with Action Comics Superman and Wonder Woman, not as far from Majestic's mentality as they used to be. I still think it would be cause for concern though. The bigger reason however is one that's not in the world of the comics but in the eyes of the fans. Superman kind of has to be the top dog of DC when it comes to flying bricks, so having someone like Majestic in the same world as him would almost guarantee that Majestic can't be as powerful as he's been in the past.
To sidestep both these issues, I think making Majestic the hero of Khera in the same way that Adam Strange is the hero Rann would be the best way to do it. This way, Majestic could be exactly who he is just somewhere else, and sometimes GL, JL, Stormwatch, or even Legion books could have stories that take place in that sector of space and Majestic would be the defender of that planet. And since he's never in the spotlight long, he wouldn't have to be dumbed down or nerfed so others wouldn't look bad, and since he's in his own society and it works, other heroes may have issue with how he functions, but they wouldn't rightly be able to change it. There could be times when Majestic leaves Khera to come to Earth for some reason if people want to see him in the normal world and interact with things and heroes there. I think it would be cool if the Kherans rejected the authority of the Oans so their planet doesn't have a GL that patrols it and also if Majestic appeared not only in the present but also a thousand years in the future in Legion books (and maybe his people visited Earth like they did in WS and some of them appear in Demon Knights as warriors or even gods, Majestic especially). Majestic could be everywhere, just not on modern DC Earth for any significant length of time.