MK did NOT need more crowds and IMHO this could have been the worst place to put the Frozen princesses -- let's drop a new 3 hour queue for a 1 minute M&G less than 100 yards away from a newer 3 hour queue (Mine Train) for a 2 minute ride. Without FP+ which will be hard gets, that's a lot of waiting for 3 minutes of meaningful activity. Well done next gen of Crowd Control...
I believe the Frozen princesses should have stayed at Epcot but maybe just move the M&G somewhere easier to manage. WoL like the OP said not a bad idea, but a big issue it is used 5 months a year for Festival space. Maybe part of Innoventions, the Odyssey, or World Showplace. Epcot can absorb crowds, has many light days, and MK this is just not so -- for me M&G should have stayed somewhere in Epcot.
DHS could have made sense after SWW is over -- a lot of empty buildings and the lowest attendance of the four parks Stage one near TSMM, the former Sounds Dangerous location could have been themed inside, FP+ added to the doors. Maybe someday when American Idol winds down we could get a Frozen stage show in there, with very low AC