I think this is a quality of life change that has been long overdue for Magmus, it makes much more sense that Magmus' ult is cast time instead of channeling.
this has directly been lifted from the last Dota 2 patch where they implemented the same change on sand king, and the reception from the community (including me) for this one change has been phenomenal. Playing sandking is a dream now.
Magmus is a hero who's playstyle revolves all around game sense and patience, but if you press that R button, that all goes out the window as you basically HAVE to go in or you waste a very valua