All the signs point to Boris Johnson accepting some version of a Northern Ireland-only "backstop" in the hope that he can sneak a withdrawal deal through parliament at the last minute. He may not succeed. If he does, the DUP will have to be offered a fig leaf. But, if Johnson tries this, he will confirm that the sovereignty of the British state in Northern Ireland is too weak for even a Conservative government to be willing to take the province out of the Single Market without the approval of Dublin and the EU.
In a new Full Brexit Long Read, Analysis #40 - The Flaw in the Crown, Peter Ramsay explains that Dublin and the EU have been able to dismiss reasonable legal/technical solutions to the problem of customs control, and to insist on the "backstop", because Britain lacks sufficient political authority in Northern Ireland to force them to negotiate seriously. He identifies the fundamental reason for the weakness of British sovereignty in the province, and argues that if Brexit is really to revive popular sovereignty in Britain, then Ireland needs to be reunited in a single republic. He also suggests that, without a vigorous campaign for reunification, a Northern Ireland-only backstop risks worsening the sectarian stasis that is paralysing government in Northern Ireland under the Good Friday Agreement.
Analysis #40 - The Flaw in the Crown: Why Popular Sovereignty in Britain Means Reunification in Ireland