The FOV is not actually locked.
You can change it in-game with a drop-down box found under [Graphics Settings > Advanced > Field of View]
Unfortunately, it seems that there are only preset options, which include [30, 60, 70, 80, 90 (the default), 100, 110, 120, 130]
--edit--
also it seems like we can edit the FOV in the config file
it might be a placebo i haven't thoroughly tested yet, but the setting is there