I doubt we'll visit it but it could well have an effect on the situation in Ferelden in some way. There was no mention of the silver order of knights that the Warden founded but I'm hopeful that if you saved both then it is assumed that you not only upgraded the Keep itself but also the soldiers manning it. If so, I hope that we meet some of them in game since I always imagined them looking pretty magnificent in their silverite gear.
I upgraded everything for the keep, I even had Wade make the special armor and Bow, I hope that there is some effect on it because it's a huge keep. I also hope that you do not have to fight with the Wardens because I simply would not be able to do that. But yeah seeing the whole army in the silverite armor, or the huge granite walls still standing would be awesome. Or maybe you can have the keep as one of your strong holds becuase I know there have been videos of you having strong hold across both Fereldon and Orlais. One can only hope right?
I know we will soon see, BUT it is not soon enough 