I feel that kind of more chaotic, less tight mechanics is actually found more within the realm of normal content and not just as evidenced by M2 NM. Those encounters don't require people to perfectly fit a square into a square else everything blows up. A mechanic that's made its big come back is the bullet hell type found in the lvl87 Dungeon (2nd boss) and the lvl100 Dungeon (last boss) for example, which was previously found in a less chaotic pattern in Barbariccia NM, and also in criterion Rokkon (first boss). But even then just AoEs being tossed around randomly, on players or on the ground, has been the bread and butter of normal modes because they're very basic in a way to understand and don't require excessive, mechanical execution to solve the more complex puzzles with less solutions often found in savage. In fact, the more complex a mechanic, the more it tends to narrow down to single possible answers (that can require a lot of thinking or be solved with a single trick, doesn't matter), which is not something that would mesh well with casual modes.

Since everybody agrees that if there is one thing that FF14 lacks, it's midcore content gameplay and I do feel that this kind of gameplay but more involved could prove interesting to fill up the much needed midcore niche. For instance, that's what Criterion normal (ex) should have been in my opinion, because its savage version is pretty much the same with more constraints asking you to play perfectly, but the content is essentially the same. Just looking at the trash in criterion, and this would be absolutely perfect for midcore content. It's not hard, it has more moving parts and violence involved than what you'd find in casual dungeons. Why are the bosses suddenly on the level of ex/savage encounters then??