I have a hard time seeing Gurriel traded as well, given the fact that the only legitimate MLB outfielders on the roster at present are Gurriel and Springer. Having to find 3 outfielders in one offseason (the team presently doesn't have a proper 4th outfielder as well) is a pretty tall order.
Gallo might be a passable 4th outfielder target if the team can find a legitimate center field option to replace/backup Springer. Gallo likely can't play a passable center field due to declining foot speed. I'm curious to see if he's helped out that much by the shift ban. He only manages to put the ball in play during less than half of his plate appearances and the k rate is approaching 40%, so the shift ban might only add a handful of extra hits for him. Ultimately I'm not sure if the team would simply be better off playing Biggio in the outfield a bit more as he has also may see a bump in his numbers from the shift ban and has a similar offensive profile to Gallo (high k/high walk, low batting average etc.).