So far it would seem that Avalanche Studios has listened to fan feedback after Just Cause 3, and is creating a more purposeful and deep sandbox with the upcoming Just Cause 4. However, as many games seem to have these days, we still can't quite escape in-game purchases, or microtransactions.
Recently the game was rated by ESRB, and in the rating description it's been revealed that the game will include "in-game purchases", meaning we might see these microtransactions in some form.
Of course this doesn't necessarily mean randomised rewards or microtransactions that alter the balance of the of the progression, but there will be some. Is that a deal breaker for you?