Sounds like you picked a good model. At least you won't be chasing parts like the extended mag tube and 3 position collapsible stock to make it right. It will be worth waiting for. I have the same 11721 and was lucky to find a new one for a good price in stock on Gun Broker last November.
I've added a Scalarworks SYNC mount with a Trijicon RMR, an IWC front light/sling QD mount with a Surefire M300C (500 lumens) and the IWC bolt on rear QD mount with a Blue Force Gear Vickers sling. I also added a GG&G charging handle and bolt release and a set of Wolff mag springs and trigger pack springs from FFT. I really can't think of anything else I would add... maybe a set of night sights?