Well, while I can now load the initramfs from U-Boot any attempt to boot it so far ends in no further output after starting kernel.
(IPQ) # usb start
(Re)start USB...
USB0: Register 2000240 NbrPorts 2
Starting the controller
USB XHCI 1.00
scanning bus 0 for devices... 3 USB Device(s) found
USB1: Register 2000240 NbrPorts 2
Starting the controller
USB XHCI 1.00
scanning bus 1 for devices... 1 USB Device(s) found
scanning usb for storage devices... 1 Storage Device(s) found
(IPQ) # usb read $loadaddr 0x0 0x2ccb
USB read: device 0 block # 0, count 11467 ... 11467 blocks read: OK
(IPQ) # setenv bootargs console=ttyMSM0,115200n8
(IPQ) # bootm
Image Name: ARM OpenWrt Linux-5.4.179
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 5870964 Bytes = 5.6 MiB
Load Address: 42208000
Entry Point: 42208000
Verifying Checksum ... OK
Loading Kernel Image ... OK
OK
mtdparts variable not set, see 'help mtdparts'
no partitions defined
defaults:
mtdids : nand0=msm_nand
mtdparts: none
info: "mtdparts" not set
Using machid 0x136c from environment
Starting kernel ...
Not sure, maybe that vendor U-Boot really does not allow this...