Disclaimer: This is MY perfect MMO, not THE perfect MMO, keep that in mind.
This is a list of features that my perfect MMO would have. note that i am aware that some of the existing MMO´s may have some of the features i describe in the same or similar form, no need to point me at your favorite MMO for it hehe.
This entry will only touch the PVE aspects, part 2 will be about PVP.
1) Cooperative PVE, not competitive PVE
The whole server would have to cooperate and complete the "high end" PVE spaces to unlock features for the server that actually benefitted the whole community, such as new areas, hunting grounds and even new cities or new features such as being able to build bigger shops/better forges/more housing and enabling crafters to provide better services and gear to everyone.
Furthermore, people of all levels should be able to help the high end players in unlocking said features because completing quests, killing monsters, crafting and generally interacting with the lower level zones content at the appropriate level would give stackable buffs inside the high end zone that in the long run would assist said high end players in defeating the bosses and unlocking the content, and all and every player that contributed either to the kill or the buff building would get rewards.
Bosses would be massive and would require the cooperation of several guilds to beat to prevent a single one from hogging all the progress, it would take time to kill one of those bosses but as mentioned before, the rewards and unlocks would be great each time making it worth the effort.
When it comes down to "loot" bosses would give to all the players that partecipated in the kill both by fighting or buff building gems that would either help them or make their characters unique.
The actual killers would get higher tier gems with awesome effects such as wings, auras or things that made their character unique.
Lower level players that contributed to the buff would receive lower tier gems based on their contribution and said gems would allow them to use special features to speed up their leveling and generally making their travels thru the lower tier zones more meaningful and fun.
There would be no level limit, but of course the zones where players could keep growing would be unlocked as the community cleared each content tier and killed the bosses.
That would make it possible for the buff to always be produced even if with the passing of time the influx of new/lower level players diminished.
It would also allow the players to see their character constantly grow without having to renounce to "high end content"
To level any efficiently you would have to party up as not only to party would offer bonuses in exp and drops but the monsters would offer enough challenge to make grouping the only effective method to level up within a reasonable amount of time.
Solores would be able to tackle some of the fields for practice or for the fun of it, but would not be able to realistically level or gear up by themselves
3) Making crafting matter
Every single item in the game except the basic gear to get started would come from the two crafting classes of the game, the blacksmiths, that would craft weapons, armors. accessories and tools, and the alchemists, whom would craft potions, food and utility items such as skill/talent resets, housing items and commodities and many more very useful items that would be necessary to the community in the long run.
Monsters however, would drop the items necessary to craft tthem and thus merchant players would see themselves forced to either trade their items for mats or purchase them off players.
Those classes would dedicate themselves exclusively to their craft and as they leveled up, instead of gaining stats, they would gain extra money when selling and lose less money when purchasing.
If a blacksmith bought back a player´s used sword for 1000 coins, the player would receive the 1000 coins in full, but the blacksmith would only lose 500 coins from it´s wallet.
Likewise, a player purchasing a new sword for 1000 coins would only pay 1000, but the blacksmith would receive 1500 coins.
This, coupled with the fact shopkeepers that sold most of their items within a fair price treshold would be contributing to the aforementioned high end buffs and would be rewarded by progressively obtaining more materials per purchase ( player selling 100 ores, smith receiving 250 instead) to help them to further develop their craft, would hopefully prevent inflation and economy breaks as players selling too cheap or too expensive would not get any bonus and be outresourced/skilled by fair merchants.
Merchants would be able to continue selling/buying their products offline to allow players that wanted to play both types or simply could not be on to keep providing their services but doing so would grant you no exp to prevent people from using craft profressions as gear/money making offline bots.
Adventuring players would obtain bonuses and discounts when selling and trading with merchants of the appropriate level, to prevent popular smiths / alchemists from hogging all the work and preventing new players to become merchants as well.
To prevent new merchants to be left behind as time passes, players making new merchant characters after content tiers have been cleared, would start with their craft skills leveled to the very basic level of the current content tier and with some token coin (they would later have to repay to the bank" to get themselves ready and started to buy and sell, allowing them to get right into the "action".
Combat would be action based to let the player´s skill shine, but monsters and monster packs should be agressive and difficult enough to encourage group play to defeat them in efficient manners.
Players and guilds would be able to have and build up housing areas that would give them minor buffs on the field and would allow them to relax and enjoy some time with the people, guildmates or party members they decide to invite .
And this is about it when it comes to PVE basic features, although i may edit and add a few new things in the future.