It seems the most generalizable workaround for kill text through end of line is:
- Position cursor
- Hit enter create a new paragraph
- Shift+end
- Backspace.
I've been using shift+end followed by shift-left for years, but I found a case where it does not work: outline view.
As observed in the question, Office interfaces greedily grab linefeed/carriage returns, and this behavior is recapitulated when hitting shift+end in Word's outline view. However, outline view has a quirk that breaks the usual workaround: any action that selects the end-of-paragraph will concommittantly select the entire bullet/paragraph. This remains true when you've unselected "smart selection" options in the File->Options->Advanced page. Once you've selected the entire bullet/paragraph, shift+left arrow now deselects it and brings the cursor to its beginning.
The above workaround results in the desired "kill line" behavior, and it should work across Office products.
ETA: If you're not intending to delete but adding style or something, and you never use outline view, then you can replace step 4 with your something and add a step 5 which is home and backspace.