I'm not buying it.
I think you're going to see a large influx of people the week of the opening coming from Florida and surrounding states who will be coming for day trips for the sole purpose of seeing SWGE. Especially with the fact that both rides won't be open right away, I don't think a ton of people are going to be booking full vacations, in March, for the back-to-school season.
This is a ploy by Disney to turn the low-low-low early fall season into a low early fall season for the purposes of closing out their fiscal year (end of September) stronger than the previous year. Does that mean crowds will be insane? Especially at the other three parks? I don't think so. My guess is instead of seeing September-like crowds, we'll see the old January/early Feb crowds we used to see where most days are 2s, with a few 3s and maybe a mid-week 1 sprinkled in there.
I think a lot of people are freaking out over nothing.