But is he really doing that? Granted, the AHL deck plans are different and it would have avoided a lot of angst if they just did something as simple as calling it "Mark II", but that isn't a complete rewrite of the OTU.
I know that HG2 has a lot of new stuff in it for higher tech levels ranging from Anti-Matter power plants (TL20), Thrust 11 M-Drives (TL17), Jump-9 (TL18), and a variety of weapons and shields above TL16. And looking at the Tech Level tables in T5 it seems that what Mongoose has published is pretty much aligned with that. And if I recall, the original LBBs and the Core Rulebooks for MgT1, and T5 were all meant to be "setting agnostic."
Of course, he could go and realy muck things up with the 3I sourcebook, but I guess we will have to wait and see.