Almost certainly never I would have thought, although Never say........!
There was a similar unrest with Twins flying long haul across the pacific/atlantic et al. which lead to ETOPS. Although becoming massively more reliable, nothing is ever perfect and engines will always break. Therefore, who in their right mind would ever certify a single engined aircraft for long haul ops.
I dont think, (I certainly hope) we will never hear the term ESOPS!