Question about ASUS ROG Swift PG278QR

That is a rather poorly posed question. This hardware can be used together without any problems (a GTX 1080Ti has enough DP outputs and the CPU has no influence on the compatibility, but requires at least a current mainboard, with which the whole thing is no problem anyway) but I assume that it is also about whether the performance is sufficient and in this respect there is no 100% correctness but only opinions. It also depends on your needs, so you would at least have to explain what you plan to use this hardware for.

Generally speaking, this setup is overkill. You can usually only use one main screen to its full potential, because this monitor is designed for gaming and games are usually only run on one monitor, so a Swift as a second monitor is a bit too much of a good thing for my taste.

A GTX1080Ti is powerful enough to push almost all games to their limits at this resolution, as it is designed more for 4k gaming, but if you are aiming for a minimum of 120 FPS, this is a solid solution. Experience shows that the reference graphics cards are less powerful than the expected custom graphics cards, which usually have better performance and less noise with their cooling solutions, so it would be a better idea to wait for these.

Instead of the i7 6700k CPU, I would lean towards a 7600k CPU if hyperthreading is not absolutely necessary, but again it depends on the individual needs.

Yes I think so