By default the game is limited to 100 FPS, correct. There's a minimum frame time of 10 ms set, but you can change it:
Go to <Documents>\Elder Scrolls Online\live(eu) and open the file UserSettings.txt with your favorite text editor.
Now look for the line containing SET MinFrameTime.2. The number right behind will default to "0.01000000". This is the minimum time between two frames in seconds.
If you'd like the game to run at 144 Hz, set this value to "0.00694444".
You can make the number even smaller, but keep in mind that this will really just cause additional load on your CPU (assuming your system is fast enough), which in the end won't improve visual quality and only increase your energy bill.