Zodwraith

Then I wouldn't upgrade at all. Your build is balanced if aging. We all get that upgrade bug now and then when something comes along to remind us gaming rigs age worse than dogs. Mine was RDR2 and Rockstar's lack of optimization for anything that doesn't begin with "AMD". 
 
If you HAVE to scratch that itch somewhere grab a big, affordable 4k panel. Outside of gaming that high rez real estate pays off BIG and the 980ti will have no problems pushing it. Good names like Samsung and LG have 50" HDR panels for as low as $350 and that will definitely FEEL like a nice upgrade the first time you browse the web in UHD. Then they can run 1080p at 120hz when you fire up a game once in a while. (You know you want to see Farcry at least once in glorious 4k)
 
When the upgrade bug bites again because the GPU is feeling too slow for even 1080p you already have a piece of your puzzle whether your upgrade path is a new GPU or plugging a console into it. TVs make more sense than monitors if you're not gaming competitively. You get bigger, sharper results for 1/3 the cost and modern TVs have better response times than yesteryear's monitors. Worst case you have a solid 4ktv that you can put to use anywhere down the road.

I too lament the stagnation/death/end of twin GPU card setups.  It was always something I wanted to do in a special build.  A project I have been saving for a rainy day.  However it just isn't going to happen now.
 
There is just something awesome about having two of something performance related be it two GPU's, two carbies, two outboard motors or two girls, really doesn't matter what,  just having two always looks and feels awesome.

Let's not give intel any ideas on yet another platform change.