As it was told at the "Alchimie" last month, MorphOS 3.x seems to have Helios integrated into the system. But I've got no idea if it will be possible to boot from Firewire devices.

A Powermac G4 QS and a Mac mini in Target-Disk Mode are working perfectly with the current version of Helios. I tried a recent external 3,5" HD case (with a SATA port) which doesn't work, according to Yomgui it's using a different chipset which isn't currently supported. But there are some older HD cases (with PATA ports), which are working good.