Hello Pier Giovanni,
It is interesting idea to merge Processor Expert for Kinetis (par of the KDS) and LPCxpresso. I have tried slightly different configuration that described Erich in his blog post.
I have installed LPCxpresso v7.7.2 (LPCXpresso IDE Downloads | www.LPCware.com) and I have activated this installation as the Free Edition.
Because PEx for Kinetis (integrated in KDS) support GNU ARM Eclipse plugins I have installed these plugins by using Help > Install New Software... . I have used the http://gnuarmeclipse.sourceforge.net/updates link.

The LPCxpresso IDE is based on Eclipse Platform v4.4.2. Therefore I have downloaded and installed the
PEx-KINETIS-v3.0-PLUGIN-ECLIPSE_4.4 (REV 3.0.0) (see the page Processor Expert Software, Microcontroller Dr|Freescale):

Note:
The package contains freescale_updater.zip and PEx_for_Kinetis_3.0.0.zip. You need to install the Freescale updater firstly.
When you launch the LPCxpreso the default perspective is quite different. The Processor Expert windows are not visible. It can be added by using Processor Expert > Show Views command from the main menu. Windows are added and can be arranged.
A new Kinetis project can be created by using New Project Wizard (File > New > Kinetis Project).
I have created a new FRDM-K64F project without KSDK because KSDK has not been installed.
When I have set following Global Tool Path in Window > Preferences (see the screenshot below) I have been able to build the default project.

The LPCxpresso contains GBD SEGGER J-Link Debugging support by default. When you want to a P&E micro debugger (e.g. OpenSDA) you must install P&E micro GDB server driver for eclipse. You can use the Help > Install New Software... command and use the http://www.pemicro.com/eclipse/updates link to install it directly.
When you open Debug Configurations windows you can add and select GDB P&E micro debug connection or GDB SEGGER J-link debug connetction:

Note:
The default configuration of GDB P&E Interface must be updated. There must be selected the Interface, Port, Device and updated the Executable path (default LPCxpresso path: ${cross_prefix}gdb${cross_suffix}), see the screenshot above.
The default LPCxpress installation does not contains any data about Freescale Kinetis derivatives. Therefore there is not possible to see any registers in the Debug perspective. You can install the EmbSysRegView plugins that are available at the http://embsysregview.sourceforge.net/update site (use the Help > Install New Software... command).
When you start debugging, open the EmbSys Registers window (navigate to Window > Show View > Other and select the EmbSys Registers). In the EmbSys Registers window select SVD(CMSIS) architecture, Freescale vendor and the target Chip), see the screenshot below:

Summary:
The LPCxpresso Eclipse IDE can be used for installing Processor Expert for Kinetis, GNU ARM Eclipse plugins and other utilities. It seems that we are prepared for the merge.
Best Regards,
Marek Neuzil