Yes! This is what I've been saying.
Osborn started and should end the series.
For those skeptical about a returning villain. I would re assure you that his return would not be until the last half hour of the film.
I would have a different main villain, but at the end reveal that Norman Osborn has been behind all the negative happenings to peter. This can include Harry's death (making him "avenge his father's death"), to perhaps problems with MJ and their marriage. Her missing directly. The death of Gwen and her father. And Perhaps the kidnapping of peter's baby.
And norman can fight spidy in a suit and tie like in the comics, or in a new more true to the comics goblin look. That part doesnt matter.
But this conclusion is perfect for the series. I personally wouldnt want it any other way.