Re: "Scope" of licenses to be covered by SPDX
Re: " Out of this topic we just discussed (in my understanding) what could be a proper definition of “FOSS”. "
The Free Software Foundation (FSF) and the Open Source Initiative (OSI) are the two organizations which, in my opinion, define what FOSS is. Any attempt to define FOSS which do not take into account the collective wisdom and process that went into their respective license lists  would be a big mistake.
FOSS = Free and Open Source Software, which is the union of software which meets the definition of Free Software and Open Source Software.
I have seen attempts in the past to expand the definition of FOSS beyond licensing to include other parameters such as open development processes and the like. They've all been spectacularly unsuccessful. There be dragons.
In the interest of full disclosure, in addition to by day job at the Eclipse Foundation, I am also a Director of the OSI.
Eclipse Foundation, Inc.
Office: +1.613.224.9461 x228
Out of this topic we just discussed (in my understanding) what could be a proper definition of “FOSS”.