4-string infiltration in bluegrass iconography

The BIB editor writes:

A long time ago it occurred to me that the logical development of melodic banjo-playing was to drop the 5-string and fingerpicks, and change to the full-length plectrum banjo. This has not yet, as far as I know, happened in bluegrass; though in the field of Celtgrass... is it just my eyes, or has Enda Scahill of We Banjo 3 taken up the plectrum banjo as well as the tenor?

However, images of 4-string banjos are creeping into bluegrass contexts. The one above (showing a Clareen Clarenbridge tenor from Co. Galway) is used by the Song of the Mountains show, based at the Lincoln Theatre in Marion, VA. The image below (showing a 4-string with Gibson inlays) is used by Rebel Records, a pillar of the bluegrass record industry, based in Charlottesville, VA. Are these just signs of the growing vogue for Irish music, or is the bluegrass banjo world being softened up for a coming complete plectral takeover?