Oh dear... where to start?...
Well, if we didn't have a coding barrier (Or a server barrier... or even a tech and knowledge barrier!)...
I know this is quite the ambitious idea but what if we had NPCs that we could interact with (Quests/Combat/Trading/Misc.) and the world changed seasons over time and our actions, as a community, changed the world around us.
See just reading that alone is quite a bit.
Perhaps a lobby you could sit in and talk with friends before choosing between an "Action" and "Role-play" server, the action one having the things mentioned above and the role-play one being what FH is now (With fixes and more features of course).
I'll go ahead and split this into two sections now, I like action so there'll be quite a bit for that one.
---Action---
--Very large world with mountains, forests, valleys, rivers, plains... not all just 1 type either... snowy, grassy, volcanic, swampy.
Dens spread across the land that could be home to many NPCs that interact with eachother, whether it be simple trading or fighting or even just exploring as if they to were players.
--Caves and/or dungeons (as extra maps) spread across the land that anyone could explore to find things that they might be able to use that re-spawns after a short time.
--No 'Levels' of any kind, this has always been a problem with multiplayer games... ppl get ignored simply because "they're not good enough." and it always feels like a bad thing to have.
--Large complex puzzles in dungeons that simply can't be solved by 1 person alone as well as simpler ones that can, with only a slightly larger bonus (to whatever you get from dungeons. xD) for solving the more complex ones.
---Role-Play---
--A lot of maps that gradually change to new types of scenery as you go through them (from grass to grass-snow to snow and volcanic and swamp and even some unrealistic areas.)
--Much more parkour... LOTS more parkour... (easy and complex.)
--A finished "Movie Maker" o.o
---Both---
Perhaps some premium stuff ppl could buy just to show their appreciation for the game, nothing game changing, just some cool stuff like maybe a nice crown or something to show that they helped fund the game.
Whew... that would take a long time to make. xD