I have a NUC6i5SYB with integrated Iris Graphics 540. I am thinking to upgrade my monitor to a Wide Quad HD 3440 x 1440p monitor (34 inch). Is this going to work?
If you look at the specs of the Intel® Iris® Graphics 540 specs its Graphics Base Frequency is 300 MHz and its Graphics Max Dynamic Frequency is 1.05 GHz and its Graphics Video Max Memory 32GB so be aware of all that, as the Intel Iris 540 graphics is "Limited by OS to one-half of System Memory" and if your PC’s memory is low then outstretching and using your PC for increased graphics memory will overload your system and make it lag . Have a look at this Intel article and guide “Can I increase the Dedicated Video Memory for Intel Graphics?
The "Max Resolution (HDMI) is 4096x2304@24Hz and Max Resolution (DP) is 4096x2304@60Hz and Max Resolution (eDP - Integrated Flat Panel) is 4096x2304@60Hz" which should handle your monitors 3440 x 1440 resolution. Make sure that you have the latest and suitable Intel drivers as it should work.
You will not be successful via the HDMI port (it only supports HDMI 1.4b and thus is limited with UHD to 4K@30Hz), but I can attest that a full 4K@60Hz connection is possible using an appropriately-capable mDP-to-HDMI or mDP-to-DP UHD adapter.
Now, as for UWQHD, I can only say that theoretically it should work (the bandwidth is certainly there) but, since my TV cannot run at that resolution, I cannot tell you proof-positive that it will work. Hopefully someone else has tried and can tell us more.
Hope this helps,