I'm not sure they currently sell the sheet themes, but they definitely exist currently. You typically get them either as part of the monthly subscriber bonus or a preorder bonus for buying a book. Digital dice exist as either free bonuses for preorder or monthly subscriber bonus as well as one time purchase with prices ranging from $4.99 to $7.96 so anyone that doesn't think they're going to fully monetize the new VTT hasn't been paying attention to what they're currently doing..People are currently thinking in terms of $0.99 feats or virtual miniatures, and they're certainly going to sell those things, but there are also going to be things like limited edition stickers for your public-facing profile, special virtual character sheet themes (which may already be offered on D&D Beyond for all I know), skins for your virtual dice, and things like that.