SAP has now released an OSS note 2456834 - Transition Guide for SAP APO stating that "SAP APO is partially succeeded by two products: SAP S/4 HANA and SAP Integrated Business Planning (SAP IBP)".
APO has mainly 4 sub-modules - DP. SNP. GATP and PPDS. Below figure shows the high-level functionalities of each sub-module and SAP’s roadmap for these functionalities to the successor products. DP and SNP will be succeeded by IBP, GATP & PPDS will be succeeded by similar functionalities in S/4HANA.
IBP is a cloud application and AATP is a new name for functionalities of GATP in S/4HANA. Architecture, configurations, user interface for IBP and AATP are very different w.r.t APO .Hence, transition to successor products should be through new configurations i.e existing APO configurations can not be reused for IBP and AATP in S/4HANA. SAP has also clearly stated in the note that "An automated migration from SAP APO to the successor products is not possible".
It is also now apparent that the future SAP landscape for customers using APO DP and SNP will need to be Hybrid i.e a mix of On-premise (Core ERP or S/4HANA) and Cloud (IBP).
IBP has been launched few years and many customers have started using it or migrated to it. PPDS has been merged in 1610 release of S/4HANA.Some parts of APO GATP have been made available in 1610 release of S/4HANA and SAP has also provided a road map for AATP as depicted in below figure.
Rule-based ATP (RBA) with substitution functionality of GATP is used by several customers, however, that is not yet available in AATP of S/4HANA. The first version of RBA is expected in 1808 release of S/4HANA.
As of now, APO functionalities are partially available in its successor products S/4HANA and IBP. We need to wait and watch when APO can be fully migrated to S/4HANA and IBP. However, it is very clear now that SAP is recommending to plan for transition from APO to its successor products IBP and S/4HANA.