Hi Roman,
The usb_hid run scenario doesn't get stuck when booting in non-UEFI mode. I'm using the very convenient vga_log_drv (thanks to Johannes Kliemann!) the get an impression of the liveliness of the system - for reference see [1] and [2].
I'm happy someone benefits from my work :) Just some notes, I've seen you already fixed the broken include path I thought I fixed it already but apparently I didn't seem to have pushed it. Aside from that I was planning to unify my current feature branches into my genode-trabant/master and to adapt the code to the current state of the Ada runtime available in Genode (I didn't touch this driver for some time so I have to update myself about its current state). Furthermore I plan to document it a little more in this process.
I also found that with the current genode/master Nova seems to boot-loop when the debug commit is applied. I opened an issue [1] about this, but it seems that it still works with your version of 18.08.
Out of curiosity I also tried to boot Sculpt in non-UEFI mode. The system doesn't freeze when pressing FN+F11/F12 but the display brightness decreases/increases instead.
So I guess the next step is to boot in UEFI mode with VGA log output enabled and setup the nova spinner?
Afaik the vga_log_drv is not available on UEFI since the Multiboot2 framebuffer info is filled with UEFIs UGA/GOP framebuffer. You'd need to use the boot_fb with a terminal log then.
Regards, Johannes