This is why I predict that the types of atheists who go out of their way to argue with religious people will become Republicans. Ten years ago their hatred was focused on rural conservatives. Today their hatred is often focused on immigrants (especially Muslims).
This what I think will start happening over these next couple decades as well. A realignment that positions the democrats as the Party of working class whites and minorities would effectively position the GOP as being the more secular, nonreligious Party in order to appeal to fiscally centrist and socially liberal college educated whites, suburbanites and upscale minorities. The northern strategy as you called it.
Hell you even saw this with Christopher Hitchens. A self described Marxist and anti-theist who sided with the neoconservatives on the Iraq war because stopping the spread of what he called "islamofascism" was more important.
I don't know if Democrats are going to win back working class whites any time soon. But I do think that college educated whites will trend Republican once the nationalist message is carried by a more respectable standard-bearer than the orange one. Evangelicals will continue to favor the GOP, but not with much enthusiasm, and turnout among this demographic will plummet. The Democrats will make up for losing white voters with the growing minority population.
Hitchens was ahead of his time I guess. If you look at a lot of the YouTube channels that attack Islam, a lot of them started out making fun of Christianity.