I think an age of apocalypse movie would feel too much like a rehash of DoFP. It also wouldn't be wise to use Apocalypse for the first time in AoA. It would need to be explained how this character we've never seen before would have taken over North American in the absence of Xavier.
I would much rather the series end with an adaption of Fatal Attractions or X-cutioner's song.
They wouldn't have to adapt the age of apocalypse story arc (I doubt they would anyway) they would just find a way to introduce the character and make him fit in the present day instead of an alternate future. X-Men Evolution managed to create an apocalypse story arc which began in season 2 and climaxed in season 4. In XME Mesmero was the one making preparations for Apocalypse's revival. In the movie they could giv ethat role to sinister which would allow for the introduction of the Marauders.
The concept could be:
X4
Sinister and his marauders are mutants hunting harvesting dna from them and using them to empower apocalypse. Elements from the mutant massacre story arc could factor here. Whether it is just morlocks or mutants in general. Then maybe Sinister hears about a group of very powerful mutants known as the X-men. Obviously with Jean and Scott dead the classic storyline from the comics couldn't work but they could adapt it to Wolverine and Storm. Especially wolverine for his healing ability which apocalypse could need to help him regenerate after using his power.
The X-Men fight to protect the Morlocks (or whichever group of mutants) but fail to stop Sinister from injecting the genes into apocalypse. Angel dies in the film and is reborn in the X5 as Archangel.
X5
The X-Men capture sinister and question him on what apocalypse is planning on doing. Apocalypse unleashes his four horsemen with Archangel leading the charge. The X-Men in a race against time scramble to find a way to stop Apocalypse and in an epic final battle they fight him and his horsemen.
X-Men cast
Storm (Halle Berry)
Wolverine (Hugh Jackman)
Rogue (Anna Paquin)
Magneto (Ian Mcklellen)
Professor X (Patrick Stewart)
Mystique (Rebecca Romijn)
Nightcrawler (Alan Cumming)
Shadowcat (Ellen Page)
Colossus (Daniel Cudmore)
Angel/Archangel (Ben Foster)
Iceman (Shawn Ashmore)
Beast (Kelsey Grammer)
Sinister (Jeremy Irons)
Apocalypse (Lawrence Fishburne
voice)
Four Horsemen
Marauders
This would be the ultimate sending off all the original actors and would be the final chapter in the lives of the adult X-Men. The First Class sequels could explore more of the early lives of character such as Jean, Scott and Ororo.