For those interested, the crux of Friedman's argument for pursuing examples of "Concrete" Incompleteness is:
> The second rationale for pursuing Concrete Mathematical
Incompleteness preserves ZFC as the ambitious target. The
idea is that normal mathematical activity up to now
represents only an infinitesimal portion of eventual
mathematical activity. Even if current mathematical
activity does not give rise to Concrete Mathematical
Incompleteness from ZFC, this is a very poor indication of
whether this will continue to be the case, particularly far
out into the future.
> The second rationale for pursuing Concrete Mathematical Incompleteness preserves ZFC as the ambitious target. The idea is that normal mathematical activity up to now represents only an infinitesimal portion of eventual mathematical activity. Even if current mathematical activity does not give rise to Concrete Mathematical Incompleteness from ZFC, this is a very poor indication of whether this will continue to be the case, particularly far out into the future.
page 8 in http://www.math.osu.edu/~friedman/pdf/0EntireBk051411.pdf