Checkmite
Skepticifimisticalationist
I'm leaning towards fake at the moment. Aside from David Pogue's comments, none of the mainstream media seems to have picked it up, not even the more sensationalist end like the Daily Fail. Nobody official involved in the investigation has even acknowledged its existence. This suggests to me that there is nothing to pick up.
Some have said that if the transcript was fake they would have expected someone in some kind of official position to have made a public statement refuting it; but I disagree with that because, as you state, no actual media is reporting on it as genuine, so it might be that the people involved aren't really aware that the transcript is floating around on the internet, or don't care since it isn't being reported on by news outlets.
Considering the fact that OceanGate has not been publicly communicative in general about basically anything at all around this case, I wouldn't expect them to make any statements about this either.