I'm currently still using a 16:10 monitor here, and while I do have plans to upgrade to a 16:9 1440p or 4K monitor, this will not be anytime soon. In the meantime I do hope you can continue making wallpapers in the 16:10 format.
i honestly have no clue what my screen ratio is i just save everything and let the computer deal with what's coming up on the screensaver/desktop background. I say go with what you want let the download button worry about it
I find the 16 by 10 ratio still really good for alot of things including image making. Plus alot of well composed 16 by 10 background I find in 1920x1200 can easily be masked from top and bottom to be 16 by 9 (1920x1080) or cropped from the sides to be 4 by 3 (1600x1200)
The once popular 1.66:1 format for Europe Theaters is in between 16 by 9 and 16 by 10 and Disney rendered all of their CAPS animated films in 1.66:1 though they were often shown in theaters masked to 1.85:1 (16 by 9 is 1.78:1)