Based on the feedback we've received for Qubes 4.0.4-rc1, we've decided to make one additional change for 4.0.4, namely updating the kernel to at least 5.4. This means that we'll need a second release candidate before the stable release of 4.0.4. 
The official announcement for 4.0.4-rc2 will come soon. This is just an informal request for anyone willing to help test kernel 5.4 on Qubes 4.0 to do so and report any problems.  The package is already available in current-testing.  Thank you!