I looked at the live-boot diffs, the rw patch needs a minor update (9990-misc-helpers). We were always recommended to use the newest version on stable.
The problem with hooks and toram is not actually a technical one but finding a sane way to do it. There isn't a "standard" place to put hookscripts (and any dependent files like a config to copy or a deb to install automatically). In a multiboot setup some might be different between systems, others common to more than one.. I generally use a subdir of the live-media directory for the relevant system. Each use case is different, this function is dedicated for custom stuff.
Hooks are part of live-config, which kicks in just after initramfs. At that point they must be available somewhere. One solution could be, if hooks are detected with toram. then remount the usb somewhere else.
Rsync is a powerful tool with excludes, filters and whatever but can get quite complex. We got into difficulty earlier with /live directory because it can't simulate "mkdir -p", I never knew that till now and the man page wasn't clear. A second rsync line might be simpler.