I'm far from experienced enough in any world to comment on "what's hard" in a OMGjet or to pretend I have any inkling of the politics behind any of this.  I could pretend, like most people, but I don't even know what's hard in a Juneau-based 207 yet. 
I've got no dog in this fight.  I just hope that Delta is as cool to us about JS as AS is, and that the lower rates that competition brings allow more of my friends and family to come visit.  ^.^
Can't we all just A: get along, B: see what happens first without trying to get our name in the pot for "told you so" credit, C: recognize that, even if Delta has teething pains during the first season of bringing in their nice, slow 757s, they'll almost certainly get it sorted out regardless?  I mean, it's not like they've never serviced Juneau before.  I hear they're willing to accept a 35% diversion rate initially... and I imagine that if they're willing to commit the resources to solve the problem they will solve the problem.
Now about all the LLWS products designed around AS 737s and how they'll relate to the 757s, I have no idea.  To this ignorant fox, Alaska does appear, on the surface, to have some relatively unique challenges... but I also imagine Delta's ops department is a behemoth with the ability to quickly computer generate a set of approaches and special criteria for test-flying and (eventually) approval.
This whole thing reminds me of the old days of inter-service rivalries.  Amusing, useful for espirit de corps, useful when competing for the same funding base, but really, at the end of the day, a sideshow irrelevant to the task at hand.
~Fox
PS. I have to admit a bit of loyalty to AS after how well they treated me while jumpseating.  Just seem like exceptionally nice people all around.