Personally it was tough sitting through 3 movies back to back (especially considering that the theatrical release of ROTK was over 3 hours long). I can't imagine sitting through 3 movies just to see the Star Wars Trilogy. I really hope Celebration isn't going to start immediately after this screening. Anyone that goes to this is going to be 1) exhausted from sitting in the same spot for 12+ hours and 2) stinky. They're going to need a shower and some sleep.
I think it would be fun and cool if this was done in a few select cities around the whole country, but this is just to limited. And I wouldn't exactly call it a "free" screening. Since you have to be registered for CIV, your admission to Celebration covers part of the cost.
I think I've become far to cynical when it comes to anything Star Wars these days. I would've been totally excited at just the idea of this a couple of years ago (before the GOUT was announced). Now, it's no more than "meh".