Finally SAP has updated note 2188482 for the allowed hardware. Currently it is limited to the small models with 4TB and 24cores. All installations on Power9 have to be on LE (Little Endian) and HANA 2.0 SPS03.
2554012 - FAQ: SAP HANA Big Endian to Little Endian Migration for IBM Power
Is it possible to use SWPM for migrating from SAP HANA 1.0 on IBM Power to SAP HANA 2.0 on IBM Power?There are limitation while using SWPM, SWPM can only be used to migrate SAP ABAP schema all other schemas like _SYS_REPO are excluded.
So if you only need to migrate ABAP schema then you can use SWPM.
If you want to migrate other schemas it is recommended to use the migration procedure refered in SAP Note 1718576.
You want to migrate from Intel to Power? Nothing easier than that:
Q: Can I recover a HANA backup made on INTEL architecture on IBM Power architecture?
A: Backups created with SAP HANA 2.0 are compatible with both supported hardware platforms (Intel and IBM Power).
You can recover SAP HANA 2.0 using data backups and log backups created with SAP HANA 2.0 on either an Intel-based system or an IBM Power-based system.
Data backups and log backups created with SAP HANA 1.0 SPS10 or newer running on an Intel-based system can be used to recover SAP HANA 2.0 to both Intel-based and IBM Power-based systems.
Data backups and log backups created with SAP HANA 1.0 on an IBM Power-based system cannot be used to recover SAP HANA 2.0. (just use the SWPM option)