Yep, and possibly I am missing something, but - set aside the mess with the non working builds and the unavailability of a compiled working version of the bmzip (luckily provided by JFX), I see a "link" in the chain missing.
In the "old" Windows 7 instructions say that the 16 bit stub is to be stripped and that after it and before the compressed MZ there is a three byte header that is to be left, i..e. what is "fed" to your tools is including the three bytes "header". (and everything works nicely)
The "new" Windows 8 instruction talk extensively about the new 16 byte "header", with the "ID" of "BMXH" and of the meaning of the following fields , but do not clear what needs to be stripped (or what needs to be fed to the tool, and/or which tool is to be used).
And NOTHING that was posted or linked to in this thread worked (not feeding it the "whole" BOOTMGR, nor feeding it stripped of just the 16 bit stub (i.e. beginning with BMXH) nor feeding it the "raw" compressed data (i.e. beginning with the MZ).
Same goes for your newly posted tool Win8BootmgrDecomp (which seemingly does "nothing" ), I just tested the 32 bit version, I see from the .au3 source that you are looking for the leading part of the "header" you found "424D5848" or "BMXH", which should mean that - just like the JFX build of bmzip - what you feed to it is the "whole" unmodified BOOTMGR, and I can confirm that the file I am feeding it does contain that, and it is at offset 0x68A0.
Still once I have selected the MScompression.dll and the BOOTMGR, and confirmed "type 4", NOTHING happens.
If i select instead the (copy of a Windows 8 one) ntdll.dll, after some mumbling, it exits with error RtlDecompressBufferEx:0xC000242.
Can you re-check (or make a "debugging build" with some more messages in case of errors)?