Not sure, but I hope not.

it probably will not be paid content (as that would drive more people away) also in cases like CS:GO, TF2, DOTA 2, RUST ect, the content creators get paid. While legally they could probably get away with selling user created content it is seen as bad taste (especially if those users aren't compensated in some form) and they could potentially be sued or have the content requested to be taken down ((as that would violate copyright laws) its sort of the same concept behind a game designer being able to claim that they made a model for a game, even though the company may own that model, the creator must still be credited)

TL;DR
They probably wont introduce paid content or if they do it wouldn't be anything substantial like maps/game modes. Any cosmetic item/weapon would probably have the zen/gp price tag, in which case the item could potentially be purchased for money, but not locked behind a money only paywall