That would be awesome.
Or maybe something like diabolos in XI where chunks of the floor fall away throughout the fight.
or arenas that have a more 3dimensional affect. like hide behind objects to avoid a. massive gust or be on top of them to avoid a huge tidal wave. maybe under them to avoid a meteorstorm.
another irk I have is that jumping never works. even if you jump over the poison puddles in av and never step in them you still take the debuff...
Most of the old school mmos did had this. fights were a lot more random and a lot less scripted. Using its predecessor XI as an example. you had proto omega. that might use a citadel buster on a tank once in the entire fight. or 3 times in the same minute. or he might put up manashields almost back to back crippling your groups magic damage, or he might never use them giving your mages free reign.
or boss ultimates for example. you could fight suzaku in sky and find he pops his chainspell literally straight away. the next fight he might not use it till hes at 10% hp... or a byakko that might pop perfect dodge at 90% hp just when all your dps have popped there damage buffs... it took a lot more skill and adaption than just memorize a dance and win.
it even existed to a degree in xiv 1.2 with ifrit. the pattern of plumes eruption and incinerates was a lot more random. the only constraint was you never saw the same one twice in a row. in arr you know which one is coming next and exactly where the plumes will be.
