If Ni were to join ROI, would it cease to exist and join the unitary government of the Republic, or would Ireland become a federal nation (of either the four provinces, or less radically Ulster and RestOfIreland)? If it is a federation, it could keep various British public services, and it would solve the "rule from Dublin" issue.
But yeah, I think it would be quite irresponsible to hold a border poll while sectarian violence is still quite likely to flare up. I don't think it would be impossible to see a United Ireland in my lifetime, but I think any scenario involving a 50%+1 vote would not be wise. Better to try and build a case for a United Ireland that prots (by which I don't mean flag activists, but ordinary prots) can accept.
There's provision within the existing Irish constitution for allowing local legislatures which was apparently designed by de Valera to allow Stormont to be "switched" over to being part of an Irish state:
The idea
has been floated recently by a SF MEP.