[whpalmer4]

This isn't an open feature request any longer: OmniOutliner 1.1 adds the ability to split existing rows at the cursor and to add line breaks while entering text. Just tap and hold in the desired spot, tap More... in the popup, and choose Split Row or ↩. You can also copy/paste multiple rows to/from other apps, and when inbound to OmniOutliner, control whether you get multiple lines in a single row (pasting into a row) or multiple rows (paste with an entire row selected).