Agreed but to me the grub2 loopback in your tutorial is only there to serve files to grub2 (which will be used by wimboot) and then this loopback will fade away when wimboot takes over.
What I mean there is you wont see you loopack drive in your winpe.
To actually get to your iso in your winpe, you use a windows batch file which will map a network drive and then mount it with imdisk.
Wimboot does indeed create a ramdrive but this is independent of your loopback : whether you serve your file from a loopback, tftp or http, this is only under the grub2 context and is volatile.
Your loopback will be lost as soon as you jump into another kernel.
What I am looking for is to actually attach a drive from your first loader, keep it while jumping to another loader (winpe for instance) and still enjoy the drive you attached with your first loader.
Currently the only way I know is iPXE+sanhook (attach a disk and/or dvd)+wimboot OR use grub4dos + specific drivers (like e.g vbus).
I agree that loading is not the way to go and clearly too slow - attaching rather is a nice way to go, when possible.
Dont get me wrong, tutorial 145 is really nice and handy and I like the fact that you use a unique iso thru out the whole process (i.e to retrieve the wim file then to launch the setup) .
I definitely learned a lot from this tutorial 145 as well as this post around grub2 and wimboot.
In the meantime, I am playing with loopback over http and am getting mixed results ... the way the http modules handles http range request is peculiar.