Popa, Rambam’s not literally saying that they will gain the status of Leviim in the sense that they should be supported by ma’aser. He would have said that specifically if that’s what he meant. He said G-d will support them, not that the people will support them.
As for the acharonim, the book on google.books.com I cited above summarizes some of their views on these issues, which are in many cases sharply opposed to those of the Rambam.