The new metals are used in jewel crafting recipes. Some may not be in recipes that are available yet. Looking at Titanium and the fact that it's a high ranked Shadow metal, I'd hold onto it. There is obviously plans to add shadow treasure cards, since they added a slot for them, so it's possible they could be used in crafting those as well as future jewels.
Thing is right now those metals we don't know if they ever well or when they would be usable. Along with the opal reagents and treasure cards for the opal recipes there is a lot of fluff you can't use.