The way I understand it is that you will be able to have a pistol grip and mag extension on the Benelli M1014 (M4 Super 90) if the ban sunsets,
but no WORKING telestock due to 922(r). The only way around this would be to add enough US-made parts to the shotgun to consider it domestic, and I highly doubt that these parts will ever be manufactured here in the US.
You can currently only have ONE "evil" feature--a mag capacity over 5, a pistol grip, or telescoping/folding stock. The pistol grip stock and the non-functioning telestock are considered the SAME, as both have a pistol grip. Either are legal now, with the stock mag capacity. Until the ban sunsets, the only legal way to add a mag extension is to buy the field stock, which has no pistol grip. After the sunset, the mag extension will be legal as well, but a working telestock will still be a "no-no", even though the shotgun will have enough features to be considered an AW (pistol grip and mag extension= 2 "evil" features).