A 357 sig could be possible I think... Based on Glock's baby models 26,27,& 33 which is the sig. They are all the same platform, it works for them so a .40 Shield... a 357 sig... should work, I guess we'll see. Demand may play a major role as well (if the gun is able to handle it).
Storm Lake put me on a "waiting list" in case they decide to produce 9mm and 357 Sig barrels for the Shield 40. Contact them if you are interested -- if the demand is great enough the barrels will be made...