Just did a pumpkin ale this past week & put about 4 lbs of canned pumpkin mix in a big muslin bag and steeped for the last 5 minutes of the boil. I was worried about two things if mashing the pumpkin mix. (a) Stuck sparge since I did not have rice hulls at my disposal. (b) The flavor & aroma compounds would be lost in a 60 minute boil. We'll see how it turns out I guess. To me it makes sense, since you lose flavor and aroma in any early additions, I would think pumpkin would be the same way.