Since the release of the game franchise is limited to a maximum level-50. That was the starting limit for every game in the series since the first, and, this one, nothing has changed.
Presumably this will change over time. Borderlands tends to raise the level cap by an arbitrary number over time in every game in the franchise. In the first part of Borderlands the maximum level was raised from 50 to 58, then from 58 to 69, while in Borderlands 2 the maximum level was raised 11 times (up to 72).
My intuition says we could end up reaching level 80, or with a probability of an unacceptably low level ceiling of 73 (literally one step higher than in the previous main game). Time will tell.
Although with skill tree recycling, it might be a good idea to keep the maximum level a little lower. This time, each tree is more specialized, mostly (if not entirely) built using the action skill of the corresponding tree. For example, by the end of Borderlands 2, each character in a given role felt almost the same when reaching maximum level. There were no unique builds for each character.
The best way to do this is probably to introduce new skill trees each time the limit goes up, leaving room for unique builds.