Originally Posted by Duelle
I'll call this into question. To name some examples, we've had people asking for extra stats on gear, often citing FFXI's stats and not realizing the balance issues those would cause progression-wise and gear design-wise (before even getting into how such stats would affect actual gameplay). We've had people asking for Dynamis and Nyzul Isle clones, gotten them and had one (Diadem) shit on for not being a source of raid gear and the other (PotD) labeled as repetitive (despite following almost the exact same structure as Nyzul Isle sans the floors with bullshit lamp placements).
What else is there? Pankration? A horribly-designed pet battle system that with some major tweaks could have been decent but was abandoned.
Moblin Maze Mongers? A decent system that was abandoned too early and then was implemented a second time (see: Meeble Burrows) because reasons.
Campaign? We already have that via FATEs, and the only difference between the two is that FATE mobs don't one-shot you the way Campaign mobs could.
Besieged? An unsustainable model, since that (along with the original implementation of colonization) assumes a continuously high in-game population.
Assault? We have this already in the form of dungeons, just without the classisms.
This all said, I'm willing to discuss things we could actually learn and improve from XI that don't mess with progression, but such examples are few and far in between.
PS: Before anyone mentions Delve and the several hundred other events with a single word for a name, those are all pretty much the same thing, just with different names and currencies. Collect gimmick (either items or currency) => pop and kill mob => get loot or get nothing depending on RNG => repeat.