Looks like they almost did it in 2012.
According to this:
http://phx.corporate-ir.net/phoenix....742&highlight=
Polaris increased from 146,328 'On-Road Vehicles' (and my understanding is nearly all of their on-road vehicles are motorcycles) in 2011 to 240,172 in 2012.
And according to this:
http://investor.harley-davidson.com/...785&highlight=
Harley Davidson sold 233,117 motorcycles in 2011 and 247,625 in 2012.
So Polaris was within a little over 7000 bikes of topping Harley this year and based on the growth rates of both companies, it looks like Polaris is almost guaranteed to sell more than Harley in 2013.
How about that?
*EDIT* - After Hellgate's post below, I went back and re-read the report and I think I may have had it completely wrong. I was looking at dollar sales figures as units and that means I was completely wrong in my interpretation. It looks Polaris' numbers are still very small compared to Harley.