Spaghetti code is usually used as a slang term for situations where old code and newer code are essentially in different formats and rather than reformat all the old code they just find a way to make it interact with the newer code. In regards to SE this has happened in the past due to changes to game engine or intended gameplay hardware during development on multiple titles in the company's history resulting in various issues on those titles. At this point with FFXIV they can build on top of it but the original game being built around the PS3 console has essentially set a hard limit to what they can add to it. Like a plate of spaghetti they can add meatballs and other stuff to it to dress it up or improve it but eventually they're going to run out of plate.