I think one of the most immediate update SE can do is put PF in Eureka (or some sort of). Don't get me wrong, it's been a MAJOR improvement that we can now group inside the instance btw (GJ SE) but I feel this is something small that can be implemented fast and will improve the party finding experience dramatically.
With how important having a party is in Eureka, the effort to create a party must be reduced to as minimum as possible. The method right now is through adventurer list having your icon as "looking for party", as well as people shouting "LFG lvl 6 so and so dps jobs", or premade PF - these are just clunky.
Some annoyances:
Adventurer list: It's a good idea but currently it's just a mess. At least make adventurer list sortable by level (if they already do this my bad), or sort/filter people who are already in party. It's just really annoying to search through adventurer list to find the job you want and the correct level through an unsorted list.
Shouting lfg: sometimes people group you which is great, but you don't know what group you're getting (you're level 6 and people are level 4? meh). Sometimes they don't, and you start thinking "should I form a party?" but you hesitate because you'll need to find other 7 people (through adventurer list ...again, or watching the shouts until there are people with the level/job you want), and you started thinking "what if there are good parties that just didn't see my shout" - these are just clunky.
Premade PF: Have to create PF outside and find people. I mean it's not terribly inconvenient, but if any of your party member leave then it's back to the "finding party member" game inside above. Yeah you can find them again outside but you'll have to wait - it's just inconvenient.
Party finder, however, is very efficient (people who hunt A/S ranks understands). It makes party demand/supply much clearer for both people who're looking for members and people who're looking to join. List your party up, and people who're looking for groups automatically fill it up and you instantly get what you need without doing all of the above. The most you'll do is shout "PF IS UP" then people knows.
I guess I don't know how hard it is to implement PF in an instance like this. If it's too time consuming/not worth it from a developer's pov, then maybe at least make adventurer list sort/filterable.