My first reaction is that it's a reduction in cost, like any other rebate on the purchase of personal property.
If you sell your personal car for less than you paid for it, you do not have a deductible loss, but if you sell it for more than you paid for it, you do have a taxable gain, just like if you paid $12,000 for Apple stock and later sold it for $12,500.
The $10,000 in government purchase subsidies (more in some counties I've heard) just raises your chance of a taxable gain from virtually impossible to highly unlikely. (but if the subsidies go away, the used Spark market might go up around the $15k+ mark where many of the older leases set the residual)