Replied to your other post about the ability to add a 1070 card into the system, and to be perfectly honest once you've got that all set up you're looking at a very nice gaming rig that'll handle pretty much any game on the market at the moment.
The only few things I could think about, in terms of additional (and they really would be additional and not required), would be maybe getting new CPU Cooler. Stock ones do the job, but it's always nice to have some head room, and a lot of them are barely noticeable sound wise, so can help keep the system quiet. Maybe also a second SSD of 250GB or so, enough to store a couple of larger games on, to help with loading.
Again, those are if I'm being super picky with the system