The Descent to Undermountain development was so troubled and widely known in the company that the threat of being moved to the project was used as leverage at Interplay.For the technical part, probably. The engine was not designed for _that_...
I've always wondered how much the Descent to Undermountain engine diverges from the original Descent engine, because there's source ports of Doom that can play Strife, but the I have never seen anyone asking why the Descent source port doesn't do DtU.