Within PANTHER research project, we aim to develop multi-rate, multi-format, multi-reach and multi-flow terabit transceivers for data-center gateways, having the capability of flexibly controlling this enormous capacity and distributing it among independent optical flows. To this end, we combine electro-optic with passive polymers and we develop a novel photonic integration platform with unprecedented potential for high-speed modulation and optical functionality on-chip. We also rely on the combination of polymers with InP elements and the use of InP-DHBT electronics for driving circuits based on 3-bit power-DACs and high-speed TIA arrays. Using 3D integration techniques, we also aim to integrate these components in system-in-package transceivers capable of operation at 64 Gbaud, operation with formats up to DP-64-QAM and flexibility in the handling of multiple optical flows on-chip. In this paper, we present the system level vision and the technical approach for the development of these modules, and we present the concept for a thin software layer that will control the parameters of the transceivers and will extend the SDN hierarchy down to the flexible optical transport layer.