If you think there's only going to be microtransactions in the online mode you're fooling yourself. The only reason there wasn't microtransactions in GTA 5's singleplayer was because take-two didn't realize how profitable they would be.

We aim to have recurrent consumer spending opportunities for every title that we put out at this company. It may not always be an online model, it probably won’t always be a virtual currency model, but there will be some ability to engage in an ongoing basis with our titles after release across the board.

The keywords here are "It may not always be an online model"

The whole gathering resources to make your camp followers happy mechanic is absolutely ripe for microtransactions and take-two will absolutely be utilizing them.