I've seem them, I've ridden one. Had a customer stop by not to long ago with one. It's an exhausting chain of events that I have covered many, many times on other forums.
The short story, get the new SLR01.
The IMPEC debut nearly 4 years ago. Having owned an original 2003 Team Machine, the SLT01, I was in the market then. BMC had issues with the supplier of their lugs (as BMC did not produce the lugs), the frame was delayed some 2 years. They fixed the lugs. I demoed one at Interbike in 2012. I bought a Colnago C59 as no one, not even the BMC dealers in my area nor rep who frequented the RBR forums could give a straight answer, much like the engineers thasle spoke with. I liked my C59 better (where the lugs are not sandwiches).
The frame comes in 2 different geometries, race and sport. I rode the race. Bike felt light enough and did all the things you would expect, but spotty availability and no exposure from the pro's left me wondering like you, why? I have also ridden the SLR01 and RM01, both awesome machines but I had close friends who manage to keep breaking them, so I bought an S-WORKS Venge instead. If I had neither of my two bikes, I'd probably get the latest 2014 SLR01 or a SW Tarmac SL4 as I like them both equally.
The IMPEC certainly has the look, but beyond that I'd spend my top dollar elsewhere and from what everyone is saying about the latest Team Machine, and with so many pro's gravitating towards that model, seems like a no brainer.
Whats that by the stem?
My customer, with Ciamillo Gravitas cranks. (Two elusive products in one)