All the SAP add-ons should be upgraded on SAP HANA and on S/4HANA. This, however, does not cost that much effort as a new implementation. Most of the SAP service providers include these updates in the maintenance.
Have in mind, though, that the S/4HANA core covers different transactions and modules than the current SAP ERP system. Some SAP add-ons can be, therefore, dropped, since they are available only in the standard system. Consult yourself thoroughly in advance about this.
The SAP S/4HANA core brings more functionalities with itself than the core of the previous SAP ERP ECC 6.0. In some cases, however, you have to decide whether it is necessary for S/4HANA to replace some already existing add-ons. Consult yourself thoroughly in advance about this. This consulting is a part of the preliminary work for the implementation of S/4HANA.