Well Johnson just lied Jane and the DUP were stupid enough to fall for it, āthereāll never be a border in the Irish seaā 
Iām not in favour of a United Ireland, yet. NI is an economic basket case and the Southās corporate tax fiddle, while yielding extraordinarily now, is coming to an end IMO (though Iāve though that for fifteen years but with tax harmonisation etc, I really think it is now). Despite that, personal taxes are high. Ireland canāt afford to subsidise NI and while the concept of a united Island is nice and tidy, the cost will dissuade many southern voters. The two ātraditionsā up North have their own concerns that need to be resolved.
The Irish Government canāt run a piss up in a brewery, and never have been able to. Itās all the MNC tax rolling in that keeps them afloat. Despite all this money, many aspects of the public health service are dreadful, A&Es full of trollies, extraordinary waiting lists to see consultants, this is why nearly 50% of the population has private health care.
The new childrenās hospital given the green light in 2012 may be finished in 2025 with a budget that has expanded from 300m to 2.4b and rising. Work on new maternity hospital given the green light in 2013 hasnāt even started yet because the nuns wouldnāt sell the land it was to be built on to the Government. They thought they could prevent terminations in the new hospital if they were the landlords. It was quite a battle. Itās initial budget was 150m, so thatās another 2b to 3b 
The Irish public transport system is a disaster, including in the capital and there is a housing crisis with low quality, ugly apartment blocks (often build to rent and owned by foreign vulture capital firms) being thrown up everywhere.
I could go on
But I make these points for two reasons, one, Ireland could no more run a project the size of integrating North and South than they could relocate the Island to the Caribbean, two, would people in the North vote for being part of this? Plus one foot in the EU and one foot in UK could be the start of turning around their economy.
Plus with the reunification of Germany falling to bits, despite the trillions West Germany has subsidised the East with, is there a any point in embarking on another reunification adventure of two things that were never actually united in the first place. One could argue that Ireland has never been united. Anyway, one would need to look back to before the Ulster plantation of 1609.
So, IMHO the āreunificationā of Ireland is, at minimum, a fifty year project, and thatās after everyone is in agreement. The problem, as ever, will be the bloody politicians, who will cock it all up.