I see immersion  silver as being most increased demand, immersion tin number two.  Today due to fine pitch components and required flatness/uniformity not afforded by HASL, and the varying degree of nickel in ENIG.  Folks using OSP generally stay there.  
The only "hiccup" is moving to or from ENIG, it will take assembly process/material sutle/significate adjustments.  
The bottomline one word answer:  silver

Brad