Well, I did in beta...
I make use of two builds, typically on support characters (Empathy, Thermal, Sonic, Cold, FF all open up when you have a solo build.) I'm big on the second build.
Three, I'm not sure what I'll do with. Especially since the alpha slot isn't "locked."
... actually, that might be it. Build that takes advantage of whatever you have in the Incarnate slots (which means it'd get more useful in the future,) versus a non-Incarnate build and a low-level build.
Think I'll get more ideas, at least, as we get more Incarnate abilities opened up. I could see a build focusing more around those, depending on what they are.
So I am curious with Posi's message who was the first to notice that we had 3 builds available after running the incarnate missions. Not sure I will make any use of it since I rarely, if ever, swap builds but it is interesting to have an incarnate build and an "exemp" build.