Are you REALLY certain, or is it just your conjectural opinion?
I'm not saying your statements aren't true, in fact, but there's a difference between saying, "I think x", and "Records of the event show x".
As for Pierce and Roosevelt, Ellison would do well to emulate their example in deference to the country. The option is Constitutionally provided that one may simply affirm that they will uphold the Constitution, and Ellison should man up and do just that.
If we allow every Tom, Dick, and Harry to swear oath on whatever book they choose, we'll eventually have some nutbar up there taking the oath on Ayn Rand, or perhaps Mark Twain; a complete lampoon of the due solemnity and gravity of the event of assuming office.
Why did I immediately see a connection between what you can foresee and how legitimizing gay "marriage" could open the door to demands for acceptance of polygamy or any other union one could conjure up?
It's vitally important to look beyond the issue at hand. We have to look further down the road to where it could lead, in every situation.
While Ellison has the legal right to be sworn in using the Q'uran, as an American citizen who is about to become a member of one of the three branches of the American government, I would expect him to honor the long-held tradition of this country. Added to that, and from what I've read, the contents of the Q'uran do not preach a love and tolerance for all men, no matter their religious or non-religious beliefs.
The powers that be in the USA see profiling as a "not nice" practice. Guess that applies to Keith Ellison, also.