GFA was a poor deal.
It promised all parties that it actually meant their best case. It promised the nationalists convergence with the Republic because we all know that Partition was originally conceived in sin and, hence, illegitimate, and history was finally resuming its natural course with a bit of a nudge.. It promised the Unionists the status quo on the basis of dwindling majority right now and who cares about them in the future because we all know that Partition was conceived in sin etc etc.
At some point, the rivets had to start popping out. The Brexit surprise got them pinging sooner than expected, that's all.
It's funny how the claim that we can't leave the EU because of what about the border -is a reason for remaining for people who like the EU, and a reason for getting out while we still can for people who do not like it.
Brussels, London and Dublin have all turned Northern Ireland into a high stakes/high profile game when they should have played it softly softly and worked for low key, non-precedent fudge solutions. There is some justification for Dublin and London doing this -the basic integrity of their states is arguably at stake. Brussels is doing it for a duff principle -the integrity of the single market does not have to be in question because there's a small leak on the island of Ireland. If I were Dublin, I'd be very worried about how my communautaire instincts had got me into the frontline in the fight for Brussels' principles.