I understand why HM/NiM shared a lockout back in the days of KP and EV, when they also shared Rakata token drops. However, now that NiM introduces a new tier of gear, I would like to see their lockouts separated as well. After all, if the stat difference in gear going from SM to HM and going from HM to NiM is the same, then allowing separate lockouts for HM and NiM should be fine considering we have separate lockouts for SM and HM already.
In the current raiding model, there is no fear of 'doubling up' on tier tokens, and the weekly limits on commendations will take care of any concerns about earning too many comms. This also provides more end-game content for raiders to do. I enjoy doing HM progression with my guild, but I also like that I can step in and help my friends out with the SM operations if they need it. It would be nice if that could continue with HM and NiM operations as well.