BO's unilateral action creates a precedent. In the SCOTUS, conservative judges have tended to be very reticent to undo precedent -- seeing it as only slightly more egregious that that original usurpation of the Constitution that created the precedent. Roe V Wade being the standard example.
The expected conservative opinion on BO's action would be that a conservative president ought not do the same thing -- wrong is wrong, and two wrongs don't make a right. However, I think we can all agree that BO has created a template here that WILL be re-used by left leaning presidents. After a midterm election, with a lame duck congress, decree some major action and have two years for it to become the de-facto law of the land before anyone really has a shot at changing it.
I'd argue, as I think many conservative / libertarians would, that our existing "progressive" tax system is one of the greatest abuses of freedom to date in the US. Private property is the cornerstone of freedom, and while to the founders, that primarily meant land, in the modern world it is investment and income. ANY suspension of equal protection is noxious to freedom, the equal protection attack on private property, has been and continues to be devastating.
So conservatives have a dilemma. The evil genie of monarchical decree, once released, is certain to be used again and again by the freedom destroying forces of collectivism and "progressivism" as a powerful nuclear tool doing maximum damage to the fabric of the nation. Do we unilaterally disarm, or make use of this force to attempt good?
Imagine a Flat Tax, of say "25%" that replaced all other taxes including FICA. Income tax forms would be on a post card. ALL people would pay the same rate on ALL income. If put in place in the same way that BO has just done, there would be a FULL THREE YEARS (providing the president made it retroactive when he decreed it), since even after the next election, the new president / congress would not take office until it was too late to enact anything for the subsequent election year taxes. By that time, the unholy alliance between accountants / lawyers / tax preparers and the IRS would have been broken -- those folks would have been forced to find new work. Their legions of tax code svengalis adding and modifying loopholes like demons in Dante's Hell would have moved on.
Yes, such change is likely to cause havoc in the economy, but make no mistake, since the genie is now released, we all have to expect changes as egregious and worse after every midterm election. In fact, taking the bull by the horns and going big fairly early may allow conservatives a chance to tilt the table in the favor of the nation.
We owe it to the future of America to give this serious thought. It is one of the few remaining ways I can see that we can turn the tide before the last wisps of inadequate restraint on Leviathan are fully released.