Reading through some of the other threads on here (SF gone away, Voting in Border Poll, SDLP, Leo V etc), I am reminded of the witty aphorism usually attributed to Brendan Behan, that whenever Nationalists meet, the first item on the Agenda is always "The Split"

But for all the amusement to be derived from seeing 40 Shades of Green cutting stripes out of each other, what is more pertinent is that not one of you seem to get the point, which is this.
Frankly, it doesn't matter one jot how many times eg SF demand a Border Poll; or some Southern politician announces a 'road map' to Unification; or how detached Westminster is from NI; or how much pressure comes from Washington or Brussels (or anywhere else, for that matter).
For since the GFA, the Constitutional future of NI is solely in the hands of the people of NI and no-one else. Further, it is only a majority who will ever decide, whether to stay within the UK, or join a UI. All else is bluster and flannel.
And for the people to be entitled to a Referendum, then it will require the SoS for NI to be of the opinion that there may exist a majority for Unity amongst the electorate.
Which means he/she has to look first to how that electorate might vote. Basically speaking, there are two pointers.
The first is to look at voting patterns in recent elections. And as eminent psephologist Prof. Brendan O'Leary pointed out at a SF Fund Raising event in NYC no less(!) a while back, ever since the turn of the century, the "Nationalist" vote in NI, as measured by SF, SDLP and various minor parties, has plateaued at around 42-43%. Moreover, O'Leary opined that he couldn't see that changing in the foreseeable future.
Now it is fair to say that the "Unionist" vote (DUP, UUP, TUV etc) is not any higher. But if Nationalism is to get over the line, it has to muster the bulk of the "Others" (Alliance, Greens, Independents etc) to their cause. Yet if you look at their votes, they are overwhelmingly drawn from Unionist-leaning areas (East Belfast, North Down etc). Therefore in the event of a Referendum, one might expect those of them who did bother to vote, to be Unionist.
Of course, that whole vote-counting exercise is arguably a misleading one, for a number of reasons. First, people vote in elections (esp local) for individual candidates for a variety of reasons - the candidate may have a personal following; there may be a local issue which skews the vote; custom and habit; or tactical considerations ("keep Themmuns out"). Consequently a vote for a given party may not exactly reflect an individual's preference in a border poll.
And that's only those who actually bother to vote! Many, of course, never go near the voting booth, either because they're disaffected by the political process; or feel they have better things to do; or because they realise that in a heavy Unionist or Nationalist area, their individual vote won't make the slightest bit of difference.
However, as eg Brexit or the last Scottish Referendum showed, in a binary poll like we're talking about, individual votes do make a difference, meaning that many "non-voters" may be tempted to turn out this time.
So if we should be very suspicious of past elections as a guide to which way a Border Poll might go, where do we look? The answer has to be Opinion Polls. Now I know that how the question is asked can often determine the answer which is received etc, and that not all such opinion polls are entirely consistent. Nonetheless, the clear consensus basically since the GFA is that a clear majority (i.e. well over 50% +1) would vote to remain.
Why should this be? Basically because Referenda are at least as much about Identity as they are about the usual political and socio-economic factors which determine elections. And the whole point is Brexit notwithstanding, many in the Nationalist community are broadly satisfied that their Irish identity is now tolerably well recognised and protected, meaning that they are more likely to be concerned about Pensions, NHS, government jobs, DLA etc in such a vote, meaning that many will abstain, or even vote to remain - who needs the disruption, uncertainty, even chaos which might ensue from a UI vote?
Whereas Unionists look at this very differently. Namely, the only way they can preserve their own Identity is by voting to remain in the UK. For at its simplest, if there is no Union, there can be no Unionists, and if they're no longer in the UK, they can no longer be British.
And no amount of assurances of a post-UI state being a "warm house for Unionists" will persuade them to take a chance on it, why should they? It is still remembered that in 1921, the Unionist/Protestant population of the Free State was just over 10%, half a century later it was what demographers deem "statistically insignificant" i.e. under 2 1/2 per cent. (At the same time, the Nationalist/Catholic population in NI was going the other way).
Therefore even if Nationalism can maximise its own traditional vote (highly unlikely imo), it still has no hope of achieving a 50%+ majority, so long as the broader Unionist vote holds up and turns out (highly likely imo).
Which is where the paradox comes in. For every time Nationalism (esp SF) stokes up the temperature* on this issue in order to maximise their own vote, it only causes the Unionist vote to stiffen round the flag.
Which ultimately means that if Nationalism is to woo the persuadeable Unionist voters whom they need, it won't be by castigating them or telling them where they're wrong, mere honeyed words won't be enough. They will also need to demonstrate good faith behind their words, by contributing to good government at Stormont etc, at least while NI is in the UK.
Yet if they do contribute sincerely and consistently to making NI work to demonstrate their
bona fides, that will only make Nationalist waverers less likely to vote for change, while Unionists will conclude that with NI now working better, why should they vote against it?
Above all, the more successful SF is in the Republic, the more determined Unionists will be to vote to remain in the UK, since there is no way on earth that they (including me!) will ever trust our future to a UI political system which could ultimately be dominated by Shinners like the Gerrys Adams and Kelly, none whatever.
* - You know, Barry McElduff and Kingsmills, the Bobby Storey funeral, or Martina Anderson's latest "Brits Out!" outburst etc.