In the games that do support SLI I've had no issues to be honest, no micro stutter that I've noticed and it runs silky smooth. Dirt Rally should run at 4K on a single 1080 Ti maxed out but scales very nicely with two cards. Dirt 4 for some reason doesn't support SLI at all and maxed out at 4K it definitely needs it.
I will agree SLI support has been getting worse lately, Dirt 2, 3, Rally and Showdown support SLI but Dirt 4 does not even after some game updates and Nvidia driver updates, really cheesed off with codemasters/Nvidia about that.
It's surprising Nvidia isn't really doing much about it as I thought they would like to sell as many cards as they can.
SLI/Crossfire really does need a big overhaul though.
Yup all comes down to games to be honest I think as mentioned in my earlier comment. With games I play SLI Scales reasonably well and for most the part feels buttery smooth paired with a G-Sync monitor and allows higher eye candy then what one 1080Ti can do, so for myself while I did not pick up multiple GPU's for SLI in general, does work well when I do game. On the other hand, play those games where SLI does not work when you need the horsepower the downside's become apparent quickly.