He Will Not Remain in Darkness

For all the doom and gloom, Isaiah refuses to remain in the darkness because the LORD refuses to allow the world to remain in darkness.  And so, Isaiah 9 -

"Nevertheless the gloom will not be upon her who is distressed,
As when at first He lightly esteemed
The land ...in Galilee of the Gentiles."

Devastation gives way to glory and so the dawn breaks in the very region that was first to experience God's judgments in Isaiah's days.  

Does this help make sense of the fact that Matthew will highlight the fact that it was in these northern parts, filled with Gentiles of mixed races, that Jesus first proclaimed the gospel (Matt 4:12-17)?

Yes, it does.