One problem though, if you trade in your car, you probably loose 20K, and you buy another P100DL which is 10K more than your P90DL originally, you still spend 30K instead of 20K. So the best scenario is not to upgrade or upgrade when you have not taken delivery. If you already took delivery, we are out of luck unfortunately.
Another option could be to go halves with a 60/75 owner on the extra $10,000. They get a 90kW battery upgrade for $5000 and costs you $5000 less. Their old smaller battery gets recycled.