Iluv2raceit
There is an entire thread that discusses this very issue regarding GTX1080 SLI vs. Titan XP. The Titan XP won in the votes by over 80%. Reason being? Yup, the Titan XP provides more consistent performance regardless of the game being played. And max FPS does NOT tell the whole story. Even with lower FPS being shown onscreen in games, gameplay was still noticeably smoother with the single Titan XP in the vast majority of games. Also, native DX12 games (not those that were DX11, then patched to DX12) do not scale well at all when played with an SLI configuration. No such issues with a single Titan XP.
I owned a dual GTX980Ti SLI configuration and replaced them with a single Titan XP and can tell you first hand that what was pointed out in that thread is absolutely true. Yes, I could have easily bought two GTX1080s and ran them in SLI, but I knew all of the shortfalls by doing so. I have now owned the Titan XP for a few weeks and can happily say that I have found no need to buy a second one. I play games at Ultra settings at both UQHD and 4K UHD resolutions on monitors that have G-Sync (Acer X34 and Acer XB321HK) and gameplay is very smooth. Only Crysis 3 gives me issues, but that game's coding sucks (sloppy software devs) and was never properly optimized anyway. Turn off AA when gaming at 4K UHD resolution and performance jumps 30-50%! Anyone who does their homework knows that AA is an absolute waste at 4K UHD resolution anyways 
Here's the thread for your viewing pleasure:
https://hardforum.com/threads/1080-sli-vs-titan-x-pascal.1905821/page-3
Remember to keep an open mind as you don't own an Titan XP, and thus don't know first hand the difference.
SLI is not all about "scaling" or bringing up higher FPS. For anyone to think that alone, probably should consider to read up more on SLI... SLI also keeps the single card from
tanking, and helps take a lot of the load (utilization) off the 1 card, maintaining a certain FPS, of course, but not just to gain higher FPS, which everyone's #1 claim seems to be. It's not all about scaling. FYI, GTX 1080 is on GP 104, and TitanX is on GP102. Feel free to praise your Titan X, however. After all, it's the same price for 2x 1080s (no pun intended). I know I know.... "SLI doesn't scale well." Your article your presented was actually quite interesting on pages 4 and 5 on why DX12 is so bad with SLI.
Don't get me wrong. The titan is a very very nice machine. It throws me against the wall when someone's only argument is "SLI doesn't have good scaling". There is so much more for what it's good for, and not just to argue the justification for buying 2 cards, or "it doesn't scale well". I would buy 2x 1080s over 1070s. The 1080 is not a weaker card, the 1070 is. I would not SLI 2x 1070s over 2x 1080s. THat would be a mistake to me. Micro-stuttering... to each their own; Not everybody has it.
DX12, yeah...., it has a problem (a big one), which I have stated before Windows 10 even launched when everybody was all hyped about it being "better" than DX11, and I told many people, and I added it won't come out like everybody thinks it will. And, I also added that Devs will continue to use DX11 until solutions are made which will make DX12 usable. It hasn't. So, Devs will keep using DX11 otherwise. It's the same thing they did when Microsoft launched DX11, only the Devs were very skeptic on it due the failed launch of Vista, ran with DX10. The notification that Microsoft was stopping support of XP was it that "helped" make everybody use DX11, otherwise they'd still probably use it (DX9)
, and that's a real shame, the shame that they would still use DX9 and not moving forward. I'll give you a year (maybe longer) until DX12 will be smooth and capable to be used in software to where more Devs will start implementing it into their product. Once it happens though, You're going to see amazing results in SLI. Also, I will add some money on the table for the companies so far that have added DX12 into their games were paid something by Microsoft. The question you should ask yourself is what kind of improvement are you getting from DX11 to 12?
Oh ya, that whole DX12 supporting AMD/Nvidia or Nvidia/AMD video cards, mixing and matching, that's a joke in itself. It won't ever happen.
We all know AMD and Nvidia will find their own "ways" to make that not happen.