would it be just to see if it can be compiled with Laz/FPC?
Not really, the idea was to create a cross-compiler setup program inspired by
Innosetup (for me,
Innosetup is the best installer for Windows).
The very good news is that
innosetup is open-source and... uses Pascal-Delphi language 
A big opportunity for us, Lazarus fans.
My opinion : i write programs in pascal because, like c++, it is a first level code, and i would prefer to use a installer coded in pascal too. So i control everything : my app and the installer too.
why do we would want to re-create inno for window
That is not the only goal but trying to compile the original windows source code could be a good beginning

...
You are building an installer to run under Windows and only Windows - just compiling the EXE under Linux/Mac.
Sorry but i use installer for Linux and ... they like that

It is
InstallJammer but it is not pascal-source:
http://www.installjammer.com/