My bad, I wasn't running the right version of plymouth.
I just re-tested with 0.8.0~-8 and the result is slightly different.
I now see the passphrase prompt (padlock + label), I can type in my passphrase just fine and when validating it seems it's opening the luks volume but nothing happens and I get back to being stuck on a plymouth splash screen (only the ubuntu logo).
When pressing escape, I see that the luks volume was opened correctly, so that part seems to work now but something still block the boot process.
My bad, I wasn't running the right version of plymouth.
I just re-tested with 0.8.0~-8 and the result is slightly different.
I now see the passphrase prompt (padlock + label), I can type in my passphrase just fine and when validating it seems it's opening the luks volume but nothing happens and I get back to being stuck on a plymouth splash screen (only the ubuntu logo).
When pressing escape, I see that the luks volume was opened correctly, so that part seems to work now but something still block the boot process.
I'll get you a new trace.