It appears EA has added new entries into fifa16.exe. These are the steps I used to get 21x9 working again on FIFA 16 after the most recent update. I tried to include the whole process for sake of completeness. I am not going to create a trainer or upload any files but this is how you can fix it yourself.
Prerequisites
1) Download HxD for your language from
http://mh-nexus.de/en/downloads.php?product=HxD . I use the portable version so I do not have to install it. Then either extract it or install it depending on your version.
2) Download Cheat Engine from
http://www.cheatengine.org and follow the instructions on the site to install it. Then follow the included tutorial to get used to how Cheat Engine functions.
Ultrawide HexEdit Fix for FIFA 16 (Do this once until another update from EA)
1) Go to your FIFA 16 install folder and make a backup copy of fifa16.exe
2) Run HxD.exe and open up fifa16.exe
3) Click on Search then Replace in the menu
4) Enter "39 8E E3 3F" in "Search for" and "8E E3 18 40" for 3440x1440 or "26 B4 17 40" for 2560x1080 in "Replace with"
5) Change "Datatype" to "Hex-values".
6) Under "Search direction" choose "All" and click "Replace all" (it replaced 3 entries on mine)
7) Save your changes and close HxD.
8) If you have issues with the fifa16.exe file delete it and use the backup you made in step 3
Ultrawide Cheat Engine Fix for FIFA 16 (Do this each time you want 21x9)
1) Run Fifa 16 and "Alt-tab" out of it
2) Run Cheat Engine
3) Click the "Open Process" and select "fifa16.exe"
4) Click "Open"
5) Check "Hex"
6) Enter "3FE38E39" in "Value" and click "First Scan"
7) Double Click "Adress 1433A7AC0"
8) Change Value "4018E38E" (3440X1440) or "4017B426" (2560x1080)
9) Switch back to FIFA 16 which is already running and "Alt-Enter" to return to fullscreen
This should get you playing again in 21x9.
Happy gaming,
bdjace