The reason I explain this is that, although grml distributes its releases in ISO, it is very easy to put it on USB -- just copy the ISO content to USB, and it'll boot fine. This is the very reason I'm asking for an ISO release of Easy2boot. grml has the functionality that the same code can boot off from either ISO or USB without modification.
Well, that is a hybrid iso, nothing particularly "new".
You can make a syslinux based hybrid .iso *anytime*:
But also grub4dos based iso-hybrid are possible, though I don't think anyone detailed the process, particularly with newish releases/tools.
We do have some "variations" on the theme, *like*:
Easy2boot is a nice "helper" to grub4dos functionalities, the base idea is to have a "basic" Easy2boot stick and being able to easily ADD *any* OS, distro or whatever crosses your mind in an "easy" way and it actually makes sense ONLY if you have a complex list of many OSes/distros in multiboot.
For simpler multi-boot (let's say three to eight "items") or for single boot, directly using grub4dos is fast and easy as well.
Since you cannot ADD anything to a .iso (please don't cite existing .iso editors that in most cases are not actually "proper" editors) it makes little sense to have the (unfortunately complex due to the "extended features" it has) Easy2Boot "overhead".
Your grml .iso is not a good example, because it ONLY boots grml and when deployed to a USB stick it continues to ONLY boot grml (and moreover overwrites *whatever* was on the stick before).
If you prefer, a hybrid .iso is only useful if you don't have a CD/DVD available BUT you have a new (in the sense of empty) USB.
Easy2boot approach is useful if you don't have a CD/DVD available BUT you have some space on an Easy2boot stick, ADDING your new .iso to it WHILE KEEPING all the other OS's you already have on the stick (and also keeping your visually appealing menu/splash/whatever other bells and whistles you decided to use in Easy2boot)