Sure, if you could find one. It looks like the odds of finding a 6+ on launch day are going to be pretty slim.
I'm in the same boat myself. Ordered the 4.7 at 2:30a last Friday thinking I didn't want the big model. But after getting the case on Saturday - I realized it's not that much bigger than the 5. Now regretting not getting the Plus...especially if the 2 gig rumors are true.
I won't unbox my 6 on Friday until I get a feel on the Plus's availability. If it's truly limited availability, I may just return it and wait it out.