I took my mid 2012 rMBP in today and this first part is exactly what happened. So I guess I'll wait to see what happens next.
I wouldn't mind a 2015 machine but I do want a dedicated GPU in my machine.
I find myself in this same situation waiting for them to call. I'm a QLab 4 user and absolutely require discreet graphics card. Are the 2015's not discreet or they just happened to offer one without discreet graphics to those in question.