I will try to answer you questions, but you may need to be more specific.

A) Cinder already does this. Just create the root volume. The ephemeral should be created at time of launch, size specified by the instance flavor selected. I will have to double check this because I forget exactly how ephemeral storage works when you are selecting "Boot From Volume"

B) The instance will boot from the volume if the volume is bootable. I am not sure what you meant by "mount root" as that should be taken care of by your OS

C) You can set the mount point of a volume when you first attach it, however you cannot set it when you launch an instance with the "Boot From Volume" option. Perhaps you can explain further why you would like these to change, and to what would yo like them to change to?

A) Put root disk in cinder volumes: has already supported by block-device-mapping-v2 extension of nova. From the CLI, you can done through:

nova boot xxxx -block-device source=image,dest=volume,id={image_id},bootindex=0,...

Put ephemeral disk in cinder volumes is not supported, and if you just want two persistent volumes for the instance, you can just append another "-block-device" argument in the above cli command.

B) Just see A)

C) The "mount point" you mentioned should be called "bus type", and is already supported by block-device-mapping-v2 extension. Just append "bus={lun,disk,scsi}" property to the "-block-device", and if "bus=lun" or "bus=scsi", you will see /dev/sda inside instance.