I would rather like to see some rare pops like

"Wandering Merchant" who actually do wander from zone to zone along a random path (obviously have to be immune to mob aggro) and sells a few randomly selected pieces of old content related tomestone items at a discount. He disappears after making the first sale.

"Deeply Wounded Adventurer" who will pop at a random zone and location, and live for a randomly decided time. Talking to him gives you a piece of old content related tomestone item (actual item randomly decided when he pop, so you might get something absolutely useless to you) in exchange for delivering a letter to the grand company or something. Upon accepting the quest he dies and you get the item immediately. Actually delivering the letter will give you some GC Seals (in case of delivery to GC) or gil (in case of delivery to closest guards).

"Lost satchels" that contain hints of who it belongs to, and you get some tomestones in exchange for returning it to the right owner. There will be other NPCs at the same time who will accept the satchel but give you no reward because they don't really own it and just want to take advantage of a silly adventurer like you. You have to think through the hints to identify the right owner.

"Mysterious nodes" that pop at random locations for botany/mining/fishing (depending on where it pops) that will give you a mysterious flower/ore/fish if you have the appropriate gatherer level and gear. You turn it in to the relevant guildmaster for some experience (if low level) or gil and some rare materials (if level capped).

Things that can't realistically be farmed and isn't just a giveaway to all players who can be online at that time.