2018-01-09 12:04:35 UTC
I have maintained the oolite package when it was still in AUR and
remember plenty of problems with running oolite against faulty /
incomplete gnustep-core implementations .
The gnustep upstream website  lists gnustep-back as a required
package for every gnustep install .
The ANNOUNCE file in gnustep-back source code  states gnustep-gui &
gnustep-back are 2 components of the display system used by gnustep .
I feel that removing gnustep-back from gnustep-core group goes against
arch linux policy of staying as close to upstream as possible.