I doubt this would ever happen. They would have to go back through every single enemy in the game that has an AoE and add some other sort of telegraph to it. Even then, with how many mobs get pulled on average, there's so way you'd be able to deal with all the less-obvious telegraphs in time. Sure, there are some other games which have limited telegraphs (Tera comes to mind here), but those games were designed around it.

I can't count the number of times I've seen people die to obvious AoEs in bosses like Coincounter and Rathalos just because there's no orange telegraph. It works fine for bosses honestly, but with giant trash pulls, it'd turn every dungeon into a wipefest.