While the Nemo line might have been extremely long, I can guarantee you that TSMM's line will not be as long for several reasons:
a) It's a higher capacity ride
b) It's at DCA which doesn't get as many visitors in general
c) It's not the return of a classic ride
With all this talk about 6 hour lines, I think you're all overthinking it. At most, I would say the line will reach 3-4 hours on opening day. How do you avoid wasting a big chunk of your day in line?
1) Arrive early early early so you don't have to wait as long.
2) Wait until right before park closing to enter the line. You'll still have to wait a while, but since the park is about to close, it doesn't matter anyways.