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