I'm not trying to be rude, but I don't think that this would be at all in character for either Luffy or Roger. Luffy's not a hero, he's not actively carrying out anyone's will, I can't speak for Roger, but do you think that Luffy would actually destroy Reverse Mountain? That he would try and 'fix' the Grand Line in the name of the commerce of a civilization that's been dead for 800 years? Luffy doesn't give a shit, Luffy wants to be the Pirate King, he doesn't want the magnetic fields to go away, he doesn't want the Grand Line to become boring, and Oda's not about to take every wonderful place he's ever created and 'fix' them. Why not pull Skypiea down from the sky so tourists can visit!?! We'll also get rid of the World Government, total overthrow, cos that would make the adventures much more fun. Why would Luffy ruin a place he loves so much? For the commoners? Luffy doesn't give two shakes about them, he cares about his nakama and that's it. If Luffy could, he'd make it more crazy, he'd have the magnetic fields flipping the islands 360 degrees so you had to ride cyclone rivers up into the sky to get to them!
I realise that I'm probably coming across as a bit insulting, and I'm sorry about that, but I think that while well thought out, this would absolutely destroy One Piece. Rayleigh's not a revolutionary, Roger just wanted to do whatever he wanted whenever he wanted and neither of them hated the World Government, not in my eyes. They don't want to overthrow it, and Luffy really probably only wants to kill Akainu. Luffy may have inherited Rogers will, but Roger never said or did anything that indicates he had a problem with the World Government. Roger was a pirate because it let him be free, he was fine letting everyone else who wanted to live with the government stay where they were. In fact, both of them have friends amongst the Marines in Garp, Smoker and Coby. I just don't think Luffy would do it, it would be OOC.