I'm sure glad the program is underway and I can understand UA keeping all the 319s (1997 and newer), but why start mods on the oldest aircraft? Why not pick a 2002 unit in both Airbus fleets instead of 1997 units?
Work your way back from the newest first. UA was able to sell many 757s, but I assume UA isn't going to sell its "newer" 319s or 320s.