The game will not open with PvP functionality, so that all the focus can be on completing other important things.
However basic "dual PvP" is an idea I had heard interest in. Note that no concept of "balance" would exist. This would not be implemented right away, but it doesn't seem too hard so perhaps we'll see it in a stretch goal.
PvP may or may not be implemented in the future.
Balance may or may not ever exist.