My sources tell me that if the 918 quota is not spoken for at the time of production, Porsche will cut the production number.  Also, regarding resale, the 918 is a long (but good) investment.  Yes it will drop a bit during the first few years, but it will certainly regain and surpass its value beyond 3-5 years.  If you can afford it, and can hold on, you will have a sure winner.

My sources also tell me that the P1 is way undersubscribed.  But for those who can afford one, the same investment curve will apply.