The Mount & Blade franchise is enjoyed among a relatively small, dedicated group of fans. One leading reason for this uptake is the large base of third-party content from its modding community. One mod, Mount & Musket, led to the creation of a game studio, Flying Squirrel Entertainment, when the mod was picked up into an official expansion, Mount & Blade: Warband: Napoleonic Wars. Sometimes taxonomy can be proper but a little bit excessive.
Developer, TaleWorlds, builds games atop their own, proprietary engine and designs it with modders in mind. They are currently in development of Mount & Blade II: Bannerlords, a prequel to Mount & Blade: Warband. In the video, below, they explain that every feature in the video is available for third-parties. This includes painting layers of materials and foliage, generating terrain by height-maps, and tessellation.
Hopefully they also add "connect to IP"…
While the game was first announced two years ago, it is still in a "when it's done" phase. The publisher is still unknown. Paradox Interactive was attached to the first three games, and Napoleonic Wars, but are not involved with Bannerlord, according to a Reddit AMA from last year. As popular as it is, at least for what it is, TaleWorlds could even be self-publishing to digital distribution platforms like Steam, Desura, GoG, and others, but that is just speculation.