547,10(A) Where Required.
547.10(A)(1) Indoors. Equipotential planes shall be installed in confinement areas with concrete floors where metallic equipment is located that may become energised and is accessible to livestock.
Similar language applied in (2) for outdoor locations.
Absent the means of energizing the metal, you don't need an E.P.
What happens in the future is another thing entirely. Article 90 is pretty plain that the NEC is not intended to address future possibilities.
Looking at the pictures of the stable, I just don't see it being an issue.
