I don't know where the graphics are going to go to next, i just know that even mid end dx11 cards from 2010 can still run modern games on low with playable frames.. And those that they can't can still be made playable by reducing resolution, and the 970 is considered a high-end card, so?.. a decent investment. I'd just worry about when microsoft's next API [dx13?] comes out because that's going to be when you'll need a replacement and no amount of tinkering with settings or resolution can save you, but that's so far in the future at least 5 years probably more like 6-7.
Optimization gets worse and worse though, and vram might become an issue sooner than expected even for such resolutions. Aside from that, the only real issues i can see popping up is due to dx12 maxwell driver implementation much later from now. I feel like when this card is no longer sufficient it's going to be because of compatibility issues not because it doesn't have enough horsepower unless you're one of those people that needs to crank all the settings to max and buy every new AAA game that comes out, in which case this card is only going to satisfy you for a year or 2.
so all that considered...
3-4 years is a very, very conservative estimate and assumes that everything that can go wrong [optimization reaching a fever pitch of bad, compatibility problems, driver implementation constraints] will go wrong.
MSI's 3 year warranty on graphics card is a confident statement in their quality, and of course that's because they know that in all likelihood you won't need it in that time frame, but you might end up with it dying after the warranty but before you need a new one, so if an extended warranty is an option, it might be worth it if you game quite a lot. I'm not sure if they're doing that though, I don't remember that option ever existing as I never looked for one.
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