It's difficult, but possible, DC is doing it right now with a ton of books, and the ones I'm reading are great so far, just read Superman 22, and man, it's great, this is probably one of the best moments to be a Superman fan, next week Action Comics comes out, and I'm totally confident that it will be good. Green Arrow, Nighwing, Batman, The Flash, Wonder Woman, Green Lanterns, are all bi-weekly comics, that are going for more than 20 issue and keeping the quality.
So Marvel can probably do it too. I think that they will be launching too new books in Legacy, adn their price is higher than DC's, so they will be passing some tittles to montly bases.