I've had the "tacticool" stocks before; no thanks..... just not me. A synthetic, perhaps with a pistol grip, maybe, but no more of the folding, sliding, extending stuff....
If anything is added out front of the magazine for "weight", it'll be a light, like a Mag-Lite LED or Surefire. The 500 already holds 5 rounds of #4 in the tube; if I need more than that, I need air support, not more buckshot.