While DirectX is pefectly fine for Windows projects, it is out of question that a less strict binding to DirectX might open up the door to a real multiplatform engine.
This step however needs someone, who REALLy needs it and is willing to get the required money for development together.

Most people who demand things like Wii support etc. neither have the big AAA game nor the team to realistically get such a project working. No offense meant - it's simply the truth everybody should accept.