for Leap 15.4 snapshots of live media are being published. At least https://download.opensuse.org/distribution/leap/15.4/live/ currently contains files dated 21-Jan-2022.
But the newest files in the iso directory https://download.opensuse.org/distribution/leap/15.4/iso/ and the "ftp" directory https://download.opensuse.org/distribution/leap/15.4/repo/ are from 02-Jan-2022.
In order to start testing the online upgrade scenarios it would be important to get these repositories published.
Especially as Leap 15.3 uses more repositories (the backports and the sle repositories) than previous Leap releases the upgrade could also be more complicated.
It would probably be good if it is possible to test the upgrade scenario before the beta code submission deadline on 16th of February.
Just as a reminder: the upgrade to Leap 15.3 exposed some problems related to repository structure and rpm signing keys quite late.
Kind regards, Dieter