Has it been explicitly said that 2.4 will launch with a new tier of gear? All I know is that they said that a new tier of gear would accompany the new operations. To me, it is reasonable that NiM would drop the new tier given past experience. If HM dropped the new tier then it would have to require KD to complete. That just doesn't seem in-line with what we've seen from BW in the past (i.e. HM isn't necessarily accessible to the casual raider, but it is accessible to the casual guild).
I just don't see them limiting HM to the very elite guilds that have their raid members decked out in full KD already. To me it seems much more reasonable that SM would require 69s and drop 72s, HM will require 72s and drop 75's, and then NiM (somewhere down the road) requires 75s and drops the new tier. Of course this is all speculation, as we don't know what BW will actually do and I haven't even been on the PTS. It just seems this has been the method they've used in the past.
Yeah, it would be accessible by non-elitist guilds, because if HM drops the new tier, SM could drop underworld and KD, so it would be easy to get KD geared.