Offline BP is a good thing, I agree. It certainly can be good to have an AY-app for offline data.
My personal experience however is that offline data is extremely whacky and I no longer trust my smartphone ecosystem to provide me with any vital documents. Example is hotels.com whos app is said to keep everything offline, but as soon as you go flightmode, it either crashes or shows up an endless loop of "please connect to a network".
Another is "checkmytrip" which indeed works offline, but every version update wipes the entire history of flights.
Yet another is Worldmate. Works indeed very well offline. But if the master site is down or unreachable for any reason when your smartphone do have network, it syncs with nothing and wipes your content.
My paid subscription to their push notice service of delayed or schedule changed flights is extremely unreliable, yet they claim to have world class access to such data. Once they insisted my flight had a schedule change to depart 15 minutes later than the true schedule, and kept pushing this info despite flight boarding, closing and departing.
SK's SAS app allows for checkin and seat selection. Only problem is that the loaded seat map does not correspond with the actual plane setup you will fly, so either check in fails altogether or your BP is invalidated when you board and they will happily send you to the nice seat of 33F or whatever is available.
Nominated in category 'worlds most annoying flyer app' is CPH airport. It has a very reliable push notice of flight details, but opens a full screen ad every 30 second, which you need to confirm before you can continue do anything useful in the app.
So these existing flyer apps have formed my view that AY shouldn't go this way. I am happy to be proven wrong!