system won't boot anymore after upgrading to plymouth-0.8.8-0ubuntu17.1

[Maxxer]

Fresh installation with 14.04 (no updates) CD works.
After dist-upgrading system won't boot anymore.

After lots of troubling I found the culprit to be plymouth!
I tried several versions of kernel, even with backported ones (3.16, 3.19), in all cases the system wasn't able to boot anymore.

Hardware is an IBM System x 3200 M2 with LSI 1064 RAID.

I described more symtomps here:
http://ubuntuforums.org/showthread.php?t=2286434
http://unix.stackexchange.com/questions/214368/ubuntu-14-04-not-booting-after-kernel-startup
http://askubuntu.com/questions/643976/ubuntu14-stuck-after-kernel-initialization

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: plymouth 0.8.8-0ubuntu17
ProcVersionSignature: Ubuntu 3.13.0-24.46-generic 3.13.9
Uname: Linux 3.13.0-24-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.11
Architecture: amd64
CurrentDmesg: [ 101.874756] init: tty1 main process ended, respawning
Date: Mon Jul 27 17:00:15 2015
DefaultPlymouth: Error: command ['readlink', '/etc/alternatives/default.plymouth'] failed with exit code 1:
InstallationDate: Installed on 2015-07-24 (3 days ago)
InstallationMedia: Ubuntu-Server 14.04 LTS "Trusty Tahr" - Release amd64 (20140416.2)
MachineType: IBM IBM System x3200 M2 -[4368K8G]-
ProcCmdLine: BOOT_IMAGE=/vmlinuz-3.13.0-24-generic root=UUID=fc639dd7-fd22-4ab0-890c-f8a21855cc47 ro
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=it_IT.UTF-8
 SHELL=/bin/bash
ProcFB: 0 radeondrmfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-3.13.0-24-generic root=UUID=fc639dd7-fd22-4ab0-890c-f8a21855cc47 ro
SourcePackage: plymouth
TextPlymouth: /lib/plymouth/themes/ubuntu-text/ubuntu-text.plymouth
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 06/11/2009
dmi.bios.vendor: IBM
dmi.bios.version: IBM BIOS Version 1.43 -[GUE143AUS-1.43]-
dmi.board.name: 4367
dmi.board.vendor: IBM
dmi.board.version: SVT
dmi.chassis.type: 17
dmi.chassis.vendor: IBM
dmi.modalias: dmi:bvnIBM:bvrIBMBIOSVersion1.43-[GUE143AUS-1.43]-:bd06/11/2009:svnIBM:pnIBMSystemx3200M2-[4368K8G]-:pvrSVT:rvnIBM:rn4367:rvrSVT:cvnIBM:ct17:cvr:
dmi.product.name: IBM System x3200 M2 -[4368K8G]-
dmi.product.version: SVT
dmi.sys.vendor: IBM