Hi there,
LTO-8 support is underway. Please raise a support ticket to find out if a pre-release TCF is available for the drive/adapter/ONTAP you are proposing. Case 2007389084 lists contacts.
Please also ensure that the HBA/config you wish to use is supported - the X1134 32Gb FC adapters for the A700s are target only and will not support direct attachment of tape drives.