This is definitely a more interesting and better thought out subject than the prior thread. I do indeed remember people modding player models in WoW to have huge spikes come out of them for PvP and even the good old FFXI trick of removing monster models to make yourself unable to target them making claims that little bit easier and quicker.

For the most part, FFXIV's core design renders this sort of stuff redundant though.

As far as PvP goes, the above has the gist of it really, marking players in PvP legitimately achieves what the spikes would have done back in the day and levels the playing field there, as well as making modding away walls such rather pointless. Half the time you can tab target around walls and corners with some camera play too, a good example of this is being able to tab target the boss in savage turns whilst the barrier is still up, just zoom right out and turn the camera 30 degrees or so to the side.

For PvE, again, waymarks and various guides already offer a handy dandy guide of where to stand.

About the only question mark in my eyes is changing the collision mapping, but then bots have been doing that for years already.