Content creators could add their own enemies, npcs, items and dungeon editor tiles.
To preface: Data driven support would mean modifications of this variety can be read and rendered/drawn by the server and client. These data-driven assets result in a new piece of content that exists as an additional object without injecting new gameplay features and instead reworking pre-existing behaviors and AI through instructional files. The only content entirely new would be the visual and audible assets that are read by the rendering engine and internal audio manager/mixer.
Unalike typical mods for other games, these data driven mods would be more like instructions that could be attached to content, like campaigns, where the game would load that particular content. Support for custom enemies/npcs (meshes and textures), character cosmetics(meshes and textures), items (meshes and textures), animations, music, and environment tiles (meshes and textures) are all the primary benefits made. This would encourage community engagement by enabling players and creators to design their own content at a more granular level.
I'm not familiar with the file types currently used within the base vanilla game, but all data driven content would be identical and behave like all the other existing files while also being the same file type for the content it pertains to.
In practice, creators would create models/meshes in a file supported 3d software, create textures in file supporting image editor, create supported music/audio files in an audio engineering software, and write/define content behavior(s) such as item components/tags or enemy components/ai in a supported data-read file wrote in the correct file type supported text/code editor of choice.
I love the current support for user-created-content, but I think it would add much appreciated longevity if this content could be aided by user created assets supported on a data-driven system.
Sorry for the overly specific and technical description. That's all. Thanks for reading!