As it says in the tin- with a POD post 1916, how could Ireland, after gaining its independence (either by the means it did IOTL, or by other means) plausibly reunite with the UK by the present day? What could possibly bring about this outcome? And what would the reunification most closely resemble- the reunification of Germany? The reunification of Crimea with Russia? Or the hypothetical reunifications of Korea and/or India?