Synthesis of NdFe12N film by Hirayama et al.  has attracted renewed interest in the ThMn12-type compounds. Although NdFe12N has large saturation magnetization and reasonably strong magnetocrystalline anisotropy , its thermodynamic instability prevents industrial applications. We have performed density functional calculations of NdFe11M for M=Ti, V, Cr, Mn, Co, Ni, Cu, Zn. We found that Co can contribute to phase stability, and NdFe11CoN has large saturation magnetization and crystal-field parameter A20 comparable to NdFe12N. We also found that the magnetic exchange coupling between Nd and Fe has a big impact on magnetic anisotropy at high temperatures, and the strength of the coupling varies significantly by interstitial nitrogenation.  Y. Hirayama et al., Scripta Materialia 95, 70 (2015).  T. Miyake et al., J. Phys. Soc. Jpn. 83, 043702 (2014).