As I see it, the USB dongle is used to exploit the system to run unsigned code by patching the kernel memory, then the "backup manager" can be installed and executed. This is actually a "tethered" jailbreak.
The question is, will it be possible to patch the kernel on the system's flash memory once the USB dongle is used to create an "untethered" jailbreak, and then it will not be required any more (until firmware upgrade).
It is theoretically should be possible to "emulate" the USB dongle hardware by connecting the PS3 to a PC using a USB cable and a custom-made device driver running on the PC. Combining this with an untethered jailbreak will be a very good solution that will be free and won't require any special hardware.