I did not reach the endgame yet, but I thought that I would share a few things here (related to end-game contents).
Firstly, I truly love the experience so far. The fact that leveling isn't as easy as on the other games of the genre make each level important and, somehow, unique. I know most people complain about the whole farming thing, but I see it as a way to practice your skills while thinking about your character's background (at least, that's how I see it).
That being said, here are a few suggestions (end-game only, I may do a post later one "Vision of a new player" or something like that).
System of leaderboard:
It is probably not a surprise (seeing the previous answers), but such a system will not only entertain the players (who want to be the very best), but it could also serve another purpose. Let me explain that briefly: every month, a new "season" starts, at the end of every season, the best three players receive something (it could be a cosmetic specially made for that occasion, rios, etc.). The goal is basically to encourage people to take part in PVP.
We could also imagine a system of arenas. If that's possible, the players who are interested in "fair fights" could talk to a PNG in each village and join some kind of queue. I believe that it could be, somehow, interesting for a certain part of the community.
PVP
As mentioned previously, I am a new player, but I already realized that PVP was a big part, not to say the biggest part, of the game. And that's why I think that a few things could be added/changed.
- Village raid: What if these raids had a direct impact on the players? I mean, of course, it shouldn't be THAT big, but what if, for instance, the players who lose their statue (I don't know the name, don't hit me), lose an outpost or something like that? Like, it could be merged with Bandit's idea (who gave a really good idea, love it).
- Arenas (already mentioned previously).
Rp contents
That includes a bit of everything. I started the game recently, but I can assure you that I can't to take part in RP missions or events. The thing is that, it would be amazing if there were more tools for that. For instance, housing for each organizations (should be expensive), etc.
Politics
I could have added to the previous part, but I think that it deserves its own thing (don't hit meeee). Basically, the politics is done by players right now, and there is nothing in game that makes it seen to the players who aren't on Discord (as I am not on my village Discord yet :(), forums, etc. Alright, let me explain:
What if the different kages could manage the politics of their village? For instance, Sand Village and Mist Village decide to become ally in order to fight against the Leaf Village or the other rogue organizations. By changing that in game, the people from these two villages wouldn't be able to attack each other (except if they have PVP on), which could encourage rp meetings between the different kages/organizations, etc. but also somehow balance the current imbalance (population of each villages).
We could also push the whole thing a bit more by adding other possibilities such as giving the possibility to each kages to add taxes to the entrance of their respective village for visitors who aren't masked. I don't know, that sounds crazy, but again, RP-speaking, that could lead to something interesting. Of course, that could be problematic for the missions, but again, these players wouldn't have to pay if they hid their identity.
Achievements
That has already been mentioned previously, but that's definitely something nice to have in such a game. Players who don't know what to do (or want to do something else) can basically open a menu and have a look at their achievements, which ones are missing, etc. I, myself, enjoy it a lot. And that could even be more interesting if a few titles were given to those who achieve specific achievements (carrot and donkey).
Dunjeons
I sincerely don't know if it is possible, but having a few dunjeons could be nice. Not only for end game players, but also for the rest of the community. Adding a Dungeon, it is also adding a new story to the game, new monsters (or not), a new experience, etc. But also, something players could do regulary. What players could get from these Dunjeons? I don't know, but I guess Weapons, rios and, why not, specific cosmetics?
Jobs
Well, that could be my last idea for now, but what about adding jobs to the game? It could start with basic jobs such as harvester, black-smith, and woodcutter then evoluate... Like, harvester could work with a new job called tailor to make new cosmetics (even recolour), etc.
Anyway, that's a bunch of ideas. Since I wrote it on my phone, there might be a few mistakes, and I am sorry for that.