Wollo,
This is not an MMO. You might want to learn the definition of one. It means a massively multiplayer online game where the players are all on the same server (also known as being in the same game). That isn't how this or most ARPGs function: even when online, you are in your own game (unless you party with others and then you are with them, and even then most games cap out at around 4 players).
The reason why MMOs often have an auction house is because the game includes a great number of resources, especially for crafting in a variety of professions. These resources typically don't drop natively while simply playing the game, and thus some players prefer to buy the materials instead of spending time on activity other than leveling/running instances, etc. In Wolcen, all the items you need (gear, gems, enneracts, gold) drop naturally in all game types and modes (solo or multiplayer, story or Champion of Stormfall, message board or expeditions). This removes the necessity for an auction house. Could it still be helpful to some players? Sure. It would definitely be a pain to program in though.
The bigger question becomes is that benefit worth all the drawbacks. As Freedfromfear mentioned, Diablo 3 tried it out and it went rather poorly. It can easily turn a game into pay to win (which most people don't want and rarely turns out well), it encourages botting, and it kind of goes against the core principal of the game: kill enemies to get better items. Items aren't good enough? Kill more enemies. Need more gems, gold or enneracts? Kill more enemies. Want to just have fun in an ARPG? Kill more enemies**.