The BIOS bootloader should not have any problems with that, in BIOS it’s easy to enumerate hard disks and read them all.
We have a limitation in the BootManager installer (not the bootloader, and not even BootManager itself): the problem there is that the installer does not know how to map a disk path (/dev/disk/…) to the corresponding BIOS drive ID (which is a value starting at 0x80 for the first hard disk, then 0x81, 82 etc for the next ones).
The only part that’s missing is implementing the B_GET_DRIVE_ID ioctl in our disk drivers. The problem is, the OS has no way to know this once booted. In BeOS, what was done was the bootloader computed a checksum of the first few sectors of each drive, and gave the OS a mapping between the checksums and the drive IDs. Then the OS could do the same checksum, and find the corresponding ID in the map.
Bootman and its installer are ready to use this info when it becomes available.