I am afraid this would be exceedingly difficult technically. Engravers run way earlier than line breaking, so the only option would be to let the engraver create both notations (with notes straddling over bar lines and with tied notes), and remove one of them later, but there is a lot of code in between that is not prepared for ignoring the collisions that will unavoidably ensue, it would have consequences on horizontal spacing, etc.
That's what I thought as well, but I think one wouldn't need to create both notations: Just create the tied notes only and, if not needed, tweak the note heads and kill some ties/other notes as late as possible. I _think_ this should be possible, involving some cheating for creating dots for situations of the type 2~ 4.
Still a mess, though, and spacing would be messed up by all the un-needed ties and extra notes.
Lukas
