Netflix's letter states it's looking into "how best to monetize sharing," which is kind of a polite way of saying "we're trying to find a way to get freeloaders to pay up.
Its first strategy, currently undergoing testing in three Latin American markets is to offer users the option to pay a smaller fee to add additional households. This way, parents in one home could pay $2.99 per month to add their kids in a different home to their account. How strongly Netflix will push such an option — how hard it will force people to it — is to be seen. The company notes that it doesn't think it can 'monetize' all 100 million account-sharees at this moment, but calls this "a large short- to mid-term opportunity."