@Walter Hinteler,
I don't think any version of the backstop will ever work. The fundamentally xenophobic idea that Britain is greater than the rest of us is woven into Brexit. Any idea that the UK should negotiate with Ireland
on an equal footing or even
care for Ireland's future is anathema for the Brexiters, who care only for their bruised national ego. And that ego demands that Ireland be "put in its place".
Therefore the Good Friday agreement is incompatible with Brexit, and therefore it is dead. The EU, including Ireland, would do well to recognise this and propose something else instead, e.g. a reunification process for Ireland.