When One Direction was on tour one of the members left the group. He left for a break that turned out to be a permanent departure. This changes the harmonies. This changes the leads on the songs. Whether One Direction liked it or not, they are forced to go into another direction.
The album is going to be something different and interesting because they are one member short. There is no telling what this will sound like. They won a Billboard award recently and they thanked the departing member Malik. One member even called him their brother during the speech so there apparently is still a lot of love for him.
The rumors, however, say that Malik is working on his own album. He will be competing against them. One Directions has millions of fans. They have mobs of fans that are so incredibly faithful to seeing them perform. Now that one member has left the groups the dynamics change. If the whole group disbands that will be the last of the heavy fan based boy band groups for now. Their next album is supposed to be a lot different. James Dondero told nexpointadvisor it will be interesting to see if they really move in a different direction. They have had a pop sound for a long time. They could venture into electronic music. They could also adapt an R&B sound to change up what they are doing.