David: I look at things and say:"Why not?"
If you have never seen beams across barlines, look at:
https://forum.noteworthycomposer.com/?action=dlattach;topic=5873.0;attach=181
The source also has the beams crossing the SysBreaks. Ravel's Pavane contains several.
Piano players often must play more than one voice at a time. The rythym of some voices is not always indicated by the barlines, hence the beam across them.
Once such a pattern is established, it makes no sense to break it for a Special Ending unless the beam would obscure the Special Ending. Although rarer, the same is true of a Flow, Key or Timesig.
Beams across clefs happen any time a clef change is needed. IMO, it would be an error to interrupt a beam for a clef. Of course NWC2's poor handling of clefs makes "text clefs" necessary, but I am looking forward to some improvement in this area.
Beaming a starting or ending rest has a simple workaround. Just layer:
!NoteWorthyComposerClip(2.0,Single)
|Note|Dur:8th|Pos:0z|Opts:Stem=Down,StemLength=0,Beam=First,NoLegerLines,Muted
|Note|Dur:8th|Pos:0|Opts:Stem=Down,Beam
|Note|Dur:8th|Pos:0|Opts:Stem=Down,Beam
|Note|Dur:8th|Pos:0z|Opts:Stem=Down,StemLength=0,Beam=End,NoLegerLines,Muted
!NoteWorthyComposerClip-End
With:!NoteWorthyComposerClip(2.0,Single)
|Rest|Dur:8th
|Rest|Dur:4th|Opts:VertOffset=2048
|Rest|Dur:8th
!NoteWorthyComposerClip-End
but why the arbitrary restriction?
Another example: Alfred Publishing's setting of Debussy's Le petit Nègre, measures 68-69