I think I found a hiden and AFAIK undocumented feature on WinNTSetup, since I never read about it on the program page, let me tell you I'm a big fan of that program, and an assiduous reader of that page, (even I was the first one to ask JFX to let me translate it, so more people could use it).
Well, if we select wimlib-imagex (libwim-15.dll) instead of Windows API during install, then automatically all files/folders on [PrepopulateList] section of the WimBootCompress.ini file located on WinNTSetup\Tools\ are applied (UNCOMPRESSED) during install (in addition to any other WimBootCompress.ini we used during Capture) and also copied that section to the new internal Windows\System32\WimBootCompress.ini so any new wim image made/captured latter from that install will keep this modded WimBootCompress.ini (including wimb's suggested changes). Then just formated VHDs and made a new set of VHDs with this approach.
I have very good news, so far I have tested 10x64, 10x86 and 8.1x64 (each one on 1.5 GB VHD) on 4 different Intel Chipset PCs and after a brief load of new drivers all Rambooted very fine, I didn't want to boot by FileDisk on any of the tested OSs in order to do not make permanent changes to them and increase the used space. Remaining free space on VHDs after Ramboot is about 1 GB.
Portability seems to be feasible without the learning process, of course we need more test on more PCs to confirm this in a total way.
I noticed UEFI_MULTI do not apply Test Mode (testsignning) on 10x86 installs, well, if Rambooting (by grub4dos menu), this is not a problem it boots very fine, but if you run it from Windows boot manager it fails, and it was required to apply Test Mode to run fine, then as this do not hurt I also applied Test Mode to internal BCD used for Ramboot, just to be consistent.
I remember on 7 and 8 x86 Signed drivers was not a so hard requirement, but unsure for 10 x86 (so many releases and changes I got lost).