I have not seen this topic posted, but it has recently made the network and online news
Just Google "$25000 rebate for heavy vehicles", there are even some specific to Model X
I am not an accountant, but mine confirms that the purchase of any vehicle with a Gross Vehicle Weight Rating aka GVWR (not curb weight) over 6000 lbs purchased by a business owner, self-employed,recipient of a 1099, etc qualifies for an tax credit of $25K in the year of purchase. Even if the car was delivered on Dec 31, 2015 it will qualify for the year 2015. In fact, even the purchase of a pre-owned vehicle applies.
It is according to the IRS Tax Code Section 179 that this is possible. https://www.irs.gov/publications/p946/ch02.html
It does not have to be a vehicle used only for business purposes, not in reality at least.
It initially was designed to provide assistance for farmers for the purchase of heavy equipment, but it is available to all who qualify.
I have introduced this topic to many car salesman who had no idea that this was a significant selling point for a large SUV.
I present this only to help others to take advantage of this tax benefit, as all of us can benefit from a little help.