As Tangle said:
"The reason all this matters for TruckersMP is because the mod has to know how to use the same API that the game is using in order to show its own HUD and menus and stuff. It has to draw on the image the same way the game is set to draw its image. If DX11 wasn't supported in MP in the next update, then you wouldn't see any of the MP text or menus when you loaded the game in DX11. That's all. Of course, making MP use a new API is just as hard as it was for SCS to make their game engine use a new API. That's the proper explanation".