Magnetic tunnel junctions (MTJ) with MgO/Fe based interfaces and out-of-plane spin direction form the basis of present-day spin-transfer-torque magnetic random-access memory (STT-MRAM) devices. They are a leading type of nonvolatile memory due to their very long endurance times and lack of reliability problems. Many semiconductor devices, such as the field effect transistor or nonvolatile memories, have undergone fundamental changes in materials design as dimensional scaling has progressed. Here, we consider how the future scaling of the MTJ dimensions might affect materials choices and compare the performance of different tunnel barriers, such as 2D materials like h-BN with the existing MgO tunnel barriers. We first summarize key features of MgO-based designs of STT-MRAM. We then describe general aspects of the deposition of 2D materials and h-BN on metals. We compare the band structures of MgO and h-BN with their band gaps corrected for the GGA band error. The different absorption sites of h-BN on Fe or Co are compared in terms of physisorbtive or chemisorbtive bonding sites and how this affects their spin-polarized bands and the transmission magneto-resistance (TMR). The transmission magneto-resistance is found to be highest for the physisorptive sites. We look at how these changes would affect the overall TMR and how scaling might progress.