Then I stand corrected, but BouT is still less demanding on the 3D side than D:OS (no ability to vary viewpoint, etc) and has simpler mechanics.

Having said that, Ogre3D was apparently used for the 2005 game Supremacy: Four Paths to Power so could likely have done a credible job for D:OS (and might even be the "problematic" middleware alluded to by Larian).

However it is difficult to hold an informed debate about Larian's development process without being an insider (heck it might be difficult even for the lead designers...) so we just have to hope a native Linux release is worth the wait.