So realistically a 1080 would still be able to play AAA games for 7 years atleast on medium settings at 1080p.
So a $700 card lasting for 7 years means $100/yr which is pretty good value.
Radeon 7970 can still play most 2017 AAA titles on high+ settings 1080p and it's over 5 years old, and it cost $550 at launch.
Regardless, high end cards are still bad for value if you aren't replacing for an extended period of time. Let's take the worst case example and assume you bought a Kepler:
Feb 2013, Top Tier (minus Titan), GTX 780 Ti 3GB, $699.
Sept 2014, Maxwell launches, still high-tier.
May 2016, Pascal launches, now mid tier.
Currently mid tier, it sells for maybe $150.
$699 - $150 = $549 cost.
Let's assume you're an Nvidia fan and stick to Nvidia.
Feb 2013, Mid-Tier, GTX 660 1.5GB, $199 (actually launched at $229 in Sept 2012)
Sept 2014, High-Tier, GTX 970 4GB, $329. You are now better than the GTX 780 Ti you would've purchased just 19 months prior.
Sell GTX 660 1.5GB, $100 (rough estimate).
May 2016 (more realistically Nov/Dec 2016, due to supply constraints), Mid/High-Tier, GTX 1060 6GB, $249. You are now way ahead of the GTX 780 Ti.
Sell GTX 970 4GB, $150 (rough estimate).
You've spent $777 - $250 = $527. If you went the GTX 780 Ti route, it would've been glorious for all 19 months. If you didn't plan on upgrading for 7 years, that would've been 65 more months were you would've had middling performance.