“But you can’t go on forever with a total fertility rate of 1.2″.

I don’t think that is actually part of the plan for many native Europeans, but for over two decades economic and social conditions have worked heavily against early marriage and parenthood.
As a relatively unskilled white male, who started working in the UK during the early 1970s, my experience has been of ever-rising costs, especially of housing, heavier taxes, increasing competition for jobs, and downward pressure on wages.
Like many of my generation, I was raised to believe that marriage and children were not to be undertaken lightly, to be responsible for my actions, to save wisely, and avoid debt.
However, that was perhaps not an advantageous pattern of behaviour for a long period of financial incontinence and state-dependency culture, in which the quickest way to get a nice flat (appartment) and regular income was to be an unmarried teenage mother, or an asylum-seeker, or even a terrorist.
There may now be a “lost generation” of the childless in the UK, who waited until they could afford a home in which to start a family, only to find that that they could never afford it, or who woke up one day and found that they were just too old, but I think the good news is that the financial incontinence seems to have been dealt a fatal blow, in which case the state dependency culture cannot long survive it.
We may soon, I hope, see a swing back to economic and social reality, and a greater need for the support of family life. I doubt that the native birthrate will actually soar as a result, but I think that replacement level will not be a problem (and replacement level is all
the UK needs, it was already too crowded a long time ago).