Baseline (Widescreen) Solution & Issues
Tribes 2 supports widescreen resolutions natively, but requires .ini editing to get proper widescreen support, otherwise it's vert-.
Go to your *\tribes2\gamedata\base\prefs\ directory and find the "ClientPrefs.cs" file. Find the following line:
$pref::Player::defaultFov = 90
Change the value to your desired FoV; 100 for 16:10 and 106 for 16:9 is recommended.
The game may not be in the proper ratio before you join a game (while you're still in observer mode). Becoming a player fixes the FOV.
You may also be returned to the default 90 FOV after you respawn, but zooming (press A) fixes it. I haven't had it happen personally.
Ultra/Super-Wide (21:9/32:9) Specific Solution & Issues
Eyefinity / Surround Specific Solution & Issues
This game is technically all multiplayer. You can use bots to simulate a multiplayer environment in certain maps (like I did).
At widescreen resolutions, all 2D elements scale, like menus and interface. The background and images are stretched. 3D models were cropped.
4k UHD Specific Solution & Issues