One option could be:

Code:
SQL> select order#, rb initial_revise, nr next_revise
  2  from (
  3     select order#,
  4            revised_by rb,
  5            order_date od,
  6            lead(revised_by) over (partition by order# order by order_date) nr
  7     from orders)
  8  where nr is not null
  9  order by 1, od;

    ORDER# INITIAL_REVISE       NEXT_REVISE
---------- -------------------- --------------------
       134 user1                user2
       134 user2                user3
       134 user3                user4
       134 user4                user5
       135 user3                user4
       135 user4                user2
       135 user2                user3
       135 user3                user6
       135 user6                user7
       135 user7                user5

10 rows selected.