Neither of these answers is very attractive, I think. One proposes a little used tag, the other to use a value of the entrance key which could be the second on the same footway if there are sliding doors before it. See this situation, for instance
Having tagged the sliding doors with
entrance=entrance/exit, it would be strange to tag the swing gate ticket barriers behind them with the same tags…
I hope this question and this discussion will eventually lead to consensus and some firm advice on the wiki about how to map these one-way pedestrian situations.