namespace MyProject
{
    public class ApplicationDbContext : IdentityDbContext
    {
        public ApplicationDbContext() : base("ApplicationDbContext")
        {
        }

        public virtual DbSet<Person> People { get; set; }
    }

    public class Person
    {
        public string Age { get; set; }
        public int Id { get; set; }
        public string Name { get; set; }
        public string SomePropertyA { get; set; }
        public string Surname { get; set; }
    }

//Global.asax.cs
    public class MvcApplication : HttpApplication
    {
        protected void Application_Start()
        {
            Database.SetInitializer(new CreateDatabaseIfNotExists<ApplicationDbContext>());

            DbMigrator dbMigrator;

            //NOTE: not the actual code, but this is what is comes down to
            if (AreaA.IsActive)
                dbMigrator = new DbMigrator(new Area_A_Configuration());
            else if(AreaB.IsActive)
                dbMigrator = new DbMigrator(new Area_B_Configuration());
            else
                dbMigrator = new DbMigrator(new Configuration());

            dbMigrator.Update();
        }
    }
}

namespace MyProject.Areas.Area_A
{
    public class Area_A_DbContext : ApplicationDbContext
    {
        public virtual DbSet<Area_A_Person> A_People { get; set; }
    }

    public class Area_A_Person : Person
    {
        public string SomeProperty_A { get; set; }
    }

    internal sealed class Area_A_Configuration : DbMigrationsConfiguration<Area_A_DbContext>
    {
        public Configuration() : base()
        {
            AutomaticMigrationsEnabled = true;
            AutomaticMigrationDataLossAllowed = true;
        }
    }
}

namespace MyProject.Areas.Area_B
{
    public class Area_B_DbContext : ApplicationDbContext
    {
        public virtual DbSet<Area_B_Person> B_People { get; set; }
    }

    public class Area_B_Person : Person
    {
        public string SomeProperty_B { get; set; }
    }

    internal sealed class Area_B_Configuration : DbMigrationsConfiguration<Area_B_DbContext>
    {
        public Configuration() : base()
        {
            AutomaticMigrationsEnabled = true;
            AutomaticMigrationDataLossAllowed = true;
        }
    }
}