tl;dr I'd like to be able to run roulettes for Anemos and Pagos crystals once 5.0 drops.
I'm pretty much a casual player. I haven't kept up with the MSQ. I think the last dungeon I unlocked is the Drowned City of Skalla. I gave up on being even a semi-serious raider when we couldn't clear T5. I only have two birds (although I have all the ponies). I still have 5 jobs in the 50s. I haven't got even the yellow script gathering or crafting gear.
Other than chasing useless achievements (I have only nine of the GC achievements left as long as they don't add any more) the only thing I'm remotely serious about is relic weapons. I've only got 26 Trials of the Braves books left to go and am about to start the light-gathering A1S marathon on my sixth Anima weapon. I enjoy how I don't have to commit to spending a certain amount of time or commit to being on at a particular time to work on the weapons. I enjoy how I can interlock activities, like running Crystal Tower to gather light for a Zodiac and getting Aether Oil for an Anima from the weekly repeatable quest at the same time. I like how I can level up the job while working on the weapon. I've even run the Vanu and Vath beast tribe quests over and over to level up some jobs, sure, but, mostly, to gather Unidentifiable bits.
Eureka presents a different way of working on relics. I've not enjoyed it quite as much as the previous systems, as it isn't as amenable to little bursts of effort and is only really fun for me with lots of people, but I've got either the weapon or the mats to make the weapon for 11 jobs from Anemos. I expect I'll get at least a couple of the Pagos ones done before 4.4 drops.
My concern is what happens after 5.0 drops. Eureka requires quite a number of people to clear NMs for the crystals necessary and I suspect there won't be many people to run chain groups once people start working on 5.0. I've already noticed that Anemos has shifted away from running the higher-level NMs to helping people with lower e-levels get experience, which is great, but makes it harder for me to hoard the crystals I'll need when I get the rest of the jobs to 70.
What I would like to see is a way to get the crystals for Eureka weapons through alternate means. At previous tiers, most of the mats for relics are available for tombstones or seals once the next expansion drops, but I'd like to suggest adding an option to roulettes to receive Eureka crystals instead of tombstones. Right now, I could get 100 Tombstones of Creation and 15 Tombstones of Mendacity for running the Duty Roulette: Level 70 Dungeons as a tank. I'd like to be able to choose to get Anemos or Pagos crystals instead. This will offer another way to get the crystals once Eureka isn't as popular, although it will probably reduce Eureka to just people trying to e-level and complete the quests. But, by the time 5.0 drops, I think most people who want to run the Eureka grind will have done so.