The fact that Gary Johnson is in favor of the FairTax is a big deal. Usually I would have no interest in Johnson, but this year is different. I, like many Americans, favor decreasing the power of the politicians in DC (and that is a reason many people support the FairTax in the first place). For people with the strongly held conviction that the government IS the problem, both Trump and Hillary are anathema. Both have an authoritarian leadership style and believe that the federal government should dictate details such as providing funding for health care for all Americans, setting minimum wages, etc.
This is the perfect time to unite and help propel Johnson into the spotlight, and thus propel the FairTax into the spotlight. Is Johnson the ideal messenger? NO. But he is A messenger. It would not take much to push him onto the debate stage (he needs only 2 more percentage points in the polls). And, there is even a slight chance that he could win the presidency as the compromise candidate if the race goes to the House of Representatives.
For those who say that they will not vote for a third party candidate because they learned their lesson with Ross Perot, I would reply that this is a completely different situation, because when Perot ran, the Republicans were fielding an acceptable candidate. This time, we truly have nothing to lose. Also, this time BOTH choices are so unpopular that people are scrambling for a way out - anyone but Hillary/Trump is the main motivator of 70% of the people polled.