Rewriting the game into something like unity instead of flash (active development/new releases would have to stop for 6-9 months with the resources deca has as of now, and that would kill RotMG because many people would quit/stop spending money on realm)
Though perhaps deca could maybe send a small part of the development team off to do the rewrite having the rest do new releases and stuff. Even then RotMG would have to be making a substantial profit for that to be fundable.
(But I think I heard somewhere that Deca only has 2 developers?)