You've got to hand it to Nadal. He was awful for most of 2015 and 2016, has been atrocious on grass since 2011, hadn't won a hardcourt tournament in 3.5 years...yet here he is winning two slams in 2017. Crazy.
The rest of the year will be interesting. Nadal might opt to protect his #1 ranking, but risks burnout. Similarly, Fed could snatch #1 (via Basel and a record 7th WTF title), though his back hasn't been right since Montreal (he didn't move well at the USO).
The 2018 AO will likely be the most anticipated in years. Everyone will be back (Stan, Djokovic, Murrary...list goes on) and you'd hope Fed and Nadal are rested enough to contend for it. Big, big opportunity for everyone else on the tour, with some big names possibly still underdone. If the courts are as fast as this year, Fed could do some damage. If they're slowed, Nadal will fancy his chances, as well as Djokovic.
Regarding future slams for Fed and Nadal, I'll go 20-18 respectively. Federer for Wimbledon (always a chance), Nadal for a French & Australian (why not?).
I think Nadal has the 2018 & 2019 seasons left, that's it. His best slam chances would likely be Roland Garros and Australia. It's hard to see the USO field being as weak as it was this year. For Fed, as long as he can manage his schedule he'll always be a strong chance at Wimbledon. I'd love to see him win one more USO, though it may be too late in the season for him these days.