X-Men: Days of Future Past, Bryan Singer is already working with Simon Kinberg, Michael Dougherty and Dan Harris on the script for X-Men: Apocalypse. We now know the next installment will be set in the early 1980s in what Singer has called an "inbetweenquel" which bridges to the original X-Men movie. Of course, with the timeline changes of X-Men: First Class and DoFP, there are absolutely no guarantees the original movie will stand as is.
Why should people be excited about Singer's Instagram photo showing the first page of the script? First thing is, the writers. In addition to Singer, Kinberg wrote the screenplay for DoFP, which has gotten great reviews, helped us forget his involvement with X-Men: The Last Stand, and will provide some style continuity for the upcoming movie. Dougherty and Harris were involved with the screenplay for X2, which was also a hit back in 2003, so the writing team has Xperience and success behind them.
The second thing, which is fodder for rampant speculation, is the mention of the Four Horsemen in the first sequence. The most famous character to come out of this group in the comics is Archangel, an altered and brainwashed version of Warren Worthington III, aka Angel. Howver, as Eric Diaz over at The Nerdist points out, the timing of the script would put the opening scene right about the point of Angel's actual birth. Who's to say something else isn't being mucked with in the timeline, but Diaz goes on to point out a very interesting possibility involving Wolverine.
Wolverine, was indeed, part of the Four Horsemen at one point, taking up the mantle of Death. Considering where DoFP left Wolverine and where he has to go to reach where his character was in the original movie, something needs to happen and Apocalypse could definitely be that something that brings back the snikt! Other popular characters that have been involved with the Four Horsemen include Psylocke, Sunfire, and Gambit. In looking back at comic history, Deathbird of the Shi'Ar also took the duties of War at one point, which could bring about a space connection, expanding the available X-Men universe into...well, the universe, which could also lead into fixing the whole Phoenix debacle from The Last Stand. With the history of using at least a kernel of the written past for inspiration, we can't be sure what's going to happen with whom, but we can also tease ourselves to death trying to figure out who is going to appear at what point in what role.
A couple of things are for sure. Wolvie needs some adamantium and just about every other character introduced so far is on the table. Is it 2016 yet?