To sum up, even after a license change, the CAPS library is not Free
Software.
I know about this, SPS wanted to prevent modifications by other people
who could use SPS to ship it with their own commercial product after
adding their own sampling format. So yes, 5.1 is a little more
restrictive than 4.2
But I think 4.2 can be included in many distributions as it's based on
MAME licence. Maybe not debian directly, but perhaps many derivatives
such as ubuntu or others RPM based distro.
In all cases, the binary library can be downloaded on sps site.