If bus/LUAS PSO doesn't cover after 2330 I wonder if this is something the Mothers Against Drunk Driving and other similar drink-driving/road-safety groups should be pushing for, at least on a targeted basis. There might still be a fare-premium for cash fare but this would be geared to additional promotion and service (minimum 20-30 mins on all routes even if that means using smaller vehicles). The sooner that people get moved out of the city centre the smaller the likelihood of incidents kicking off while people are hanging around waiting at taxi or bus ranks.
Over in these parts there is certainly a feeling that certain night routes deserve the term
"Vomit Comet" but that it's better to put up with that and try and minimise it rather than abandon the city to the grasp of the taxi industry.