Really, it's rather cheap compared to a fireworks show and seems to get a decent draw. As long as it's pulling in guests and keeping them entertained, I can see this sticking around at least seasonally. Especially at the Halloween and Christmas parties, since they may not have the castle projections during the actual firework shows for now.
Do we have any idea of how long OUAT will be sticking around going forward? I've almost been hoping OUAT would be retired or replaced with something else within a year or two, but that may be a pipe dream. I tend to think OUAT pales in comparison to CtM (especially the music) and it does seem pretty redundant now that the fireworks (for better or worse) include castle projections!