Wetstart,
I can think of a few reasons an airline would get involved with MPL. First, SMJP has already stated he's flown with some and he sees a significant difference in the quality of their skills. Second, new pilots are willing to work for less money than the experienced pilots probably will. Third, there is a significant amount of excess flight simulator capacity in Europe and those who invested many Millions in the sims would like to find a way to put that capacity to use in revenue generation through training. Many of these sims belong to airlines large enough to conduct all or most of their own training. Lufthansa comes to mind here.
My list is not exhaustive, but in light of the fact that two of the three reasons I can come up with for MPL happen to be economic, EWSD02's questions are the relevant ones. They won't be settled for most people until there are a lot more MPL pilots out there. Even then, the debate will rage on for years, just as the Modugated vs. Interbobular debate goes on ad nauseam.