Ok, this time it's really about "reimplement the baseline functionality of MS-DOS 5/6".
After booting the EDR Kernel with SvarCOM as shell, I observe the following issue:
When loading 4DOS as secondary shell (!), it's not possible to exit 4DOS (i.e. return to SvarCOM).
I don't see this with EDR command.com.
And, of course, not with MS-DOS 6.22, too.
Tested with 4DOS v8.00, but just for fun I tried a very old 4DOS (NDOS v4.03) (from Norton Utilities 8.0),
same result, so I guess it's not 4DOS-related.