I don't know... Maybe if they add another large area to act 1. But only level 5. Level 5 will give spellcasters access to level 3 spells. These include some fairly powerful spells in comparison; Fireball, Call Lightning & Protection from Energy being some of my personal favorites. Spellcasting warrior classes/subclasses get 2nd level spells. Warrior classes get an extra attack... There is a huge jump in power from level 4 to level 5... And more importantly for Larian, I would think, a huge jump in game mechanic complexity.
But leveling could definitely be slowed down a bit. Not so much the masses get irritated enough to not spend money, but right now you could easily walk out of the Druid Grove at level 5.
