Platinum is a hard one for me.

Over 50% of the use is as an autocatalyst.
http://unctad.org/infocomm/anglais/platinum/uses.htm
If electric vehicles do eventually take off (several technology advancements are close) or another autocatalyst technology is developed (http://www.platinum.matthey.com/media-room/our-view-on-.-.-./mitsui-mining-s-silver-based-autocatalyst/) then there will be a declining demand for that purpose.

However if people are prohibited from gold then investment demand will probably pick up.