Just my opinion, but I think that Fender thinks Mustangs are extremely trendy right now,
so they figure 'strike while the iron is hot, we'll start high and see who bites'.
There's the JMJ Mustang, the P/J Mustang, the American Performer Mustang, the Vintera Mustang, and the recently announced Classic Vibe '60s Mustang.
Several stores have exclusive variations on these models too.
I have two MIM P/J Mustangs, and both of them have had bad switches.
Other than that, they're made fairly well, but IMO, the pickups are nothing to write home about. I swapped them out in one of them.
That's my only experience with MIM basses though.