I have been told that we can expect a firmware update for the Canon EOS R5 sometime around the ship date for the Canon EOS R3. The EOS R3 is scheduled to begin shipping on November 26, 2021.
The firmware update will likely include added support for the RF 5.2mm f/2.8L Dual Lens Fisheye that is scheduled to begin shipping in December of this year.
The usual bug fixes are also likely. Other than that, I have no information about any additional features that may be added to firmware v1.5.0 for the EOS R5.