There's no reason airline pilots aren't issued full type ratings during their initial checkride; the "cost" argument is bunk as the standards are the same and pretty much the only differences between a PIC and SIC check are a no flap landing and circling approach. If an ATP becomes mandatory for flying 121 (and I don't think that's unreasonable) then there's even less excuse for airlines to not fully type new pilots.
I also think that AQP should become the mandatory training standard for 121, so that "training" is emphaised much more than "checking".
With that said, I was hired by Air Wisconsin with 1050tt, 50 of which was jet SIC. I also had 500+ hours of Level C/D simulator time, the vast majority of which was obtained while working for a major 121 airline training department. At the risk of sounding arrogant, CRJ training was a breeze for me due to my background and I was just as competent and safe a line pilot as somebody going through training with four times my total flight hours. Two years later when I obtained my ATP, my mechanical flying skills were not any better than they were when I was hired by ARW.
HOWEVER...I had two summers and two winters worth of experience under my belt, and that experience very likely made me a better and more knowledgeable pilot.
IMO, if an ATP becomes mandatory for flying 121 I think the minimum experience for Part 135 non-passenger operations (ie freight) needs to be reduced to 750 hours, in order to give pilots a better avenue of achieving the experience that will make them better, more knowledgeable, more experienced airline crewmembers.