It would be nice to have some kind of converter from other formats. I don't know how complicated is developement for LockOn or DCS, so I don't know if it would be possible to make an application that loads one of the standard 3d format (obj, collada, fbx...), and converts it to internal LO/DCS format.
There are many people who make planes to other sims, and they just can't afford 3dsMAX, so they are using freeware and cheap alternatives like Blender, 3dCanvas, Softimage ModTool, and many more. Most of them have enough tools to make a complicated 3d models for a simulator/game.