1. I have seen the delay you speak of. It seems to be certain systems\BIOSes. I dont know why it happens but I think it is to do with using a graphics mode menu and grub2.
2. Not sure what you mean - what happens in this black command window?
You did not follow the E2B instructions. You should use the .imgptnlbaa23 file that I provided.
In order to boot using grub2, you need to run a specific command line full of linux kernel parameters - these vary from linux version to version and from distro to distro. There is no generic way to boot linux ISOs, they are all different.
That is why most multiboot utilities need you to tell them what the ISO is based on, so that they can guess what kernel parameters are needed.
It is also why they never work 100% with very new ISOs or old ISOs, the authors have to continuously change the parameters whenever a new version is released.
Now E2B uses the partnew trick (as first mentioned by cdob). This provides a generic way to boot 99% of any and all linux ISOs (MBR boot).
So, I could write a script to auto-detect any ISO you place in a folder - but then what parameters should I use to boot it?
Every new version of every distro continuously changes them! So the script would need to detect what version each one was and have a database - or it could perhaps look for existing grub.cfg or isolinux.cfg files and try to either run them directly or parse them to make a new grub menu file.
However, grub2 does not allow disk writes (it does not even have dd so I cannot mimic a partnew command).
With my version of grub2 menu, you can add your own cfg files (as xxx.grub2 files). My menu system will automatically add the .grub2 files to the grub2 menu (in a similar way to .mnu files in E2B). So it is 'easy' to add (and delete) your own ISOs and .grub2 files.
UEFI booting will always display a 1024x768 as it boots. If you use the E2B .imgptnlbaa23 file, you will see the grub4dos menu first if it MBR boots.