I think it comes down more to a question of leverage than of weight. If you have a rated tongue weight capacity of 500 lbs, by doubling the length of the "lever" (the distance from the receiver to the ball), you cut your capacity in half. The 500 lb rating is at a certain distance from the receiver -- I don't really know how far, but it is pretty close. So, you can easily carry the motorcycle (if it isn't a big one), but if your 500 lb capacity is now effectively 250 lbs at the ball, and that is used up by the bike (my Yamaha Virago 250 weighs just under 300 lbs), you have nothing left for the trailer's tongue weight. Don't forget to factor in the weight of the rack -- close to 100 lbs.
Then the other side of leverage is that by increasing the distance from the axle
to the ball, you give the trailer a dramatic advantage in leverage against the tow vehicle. Trailer bounce and sway will be significantly more pronounced, with the corresponding negative effect on safety and emergency handling.
I might consider something like this if I had a class IV hitch, a small motorcycle and a lightly loaded Scamp
. Otherwise, I think I'd pass.