another potential issue with the growler in Colorado and i believe many other states would be the "open container" laws.
I think all you'd have to do would be secure the cap somehow (duct tape or shrinky-dink), same as a brewery.
In many states, open-container laws only apply to single-serving containers. No worries in Delaware though, we don't have an open container law for cars (passengers can drink, not drivers).
I completely agree that growlers sales won't make sense for many liquor stores. Space, setting up taps, keeping draft lines clean, training staff are all complications for the store. But nobody is forcing the store to do this either. This is legal in NY, but I know of only a few places that do it (actually, only one).
I'd hope that any store doing this would only offer craft beer that isn't available any other way. I'd be pretty disappointed if this were legal and someone offered growlers of 60 Minute IPA. It would really be for stores that want to showcase a great selection of beer.