No it won't.
The president can't introduce and pass legislation, he can only agree or veto with any bills that hit his desk.
Cain will be obligated to push hard for 999, but he is not responsible should congress fail to produce a bill.
He'll be obligated to resist all attempts to increase and further complicate the tax code, which will be a great thing.
I agree with you in substance, but perception is reality. If Cain can’t get Congress to pass 999, it will be all the soundbites in 2014 and 2016.