If Si CMOS for massive M3D is difficult due to need for high-thermal-budget processes, are there solutions that are beyond Si? In this article, we discuss two low-thermal budget approaches: Oxide Semiconductor and 2D Materials for M3D integration. By reviewing some of our recent work with IGZO-based transistors and memories, followed by our investigation of the 2D material opportunities for 3D memories, we highlight the need for new low-thermal-budget additive techniques for heterogenous multi-material integration as well as low-temperature material modification. Given the unlikelihood of “perfect materials”, new system architecture-material-device co-design intervention will be essential to capitalize on the specific trade-offs of the components.