Okay, so who here remembers that one boss fight in the Kilika Woods, where the encounter spawns kept on triggering? We had to be moved to another area so we can RP un-interrupted.
Here's an idea: Empty 2x2 areas, designed for each tileset, for DM-event/RP boss battles. No placables, but just a little terrain modifactions to help resemble the area they're fighting in. Music set to 'fighting music', on default. Just like in those FF games: the party is running around the area, the screen does that blurry motion stuff, and they're in that one fighting area. DM's can also prepare the area beforehand and teleport the party to the area. Instead of instaneously spawning an NPC that's set to guard/hostile in the blueprints and opennly attack players and/or other npcs.
RP-Boss fights and events go undisturbed. DM's have areas to prepare without having players walking in coincidence.