Whether to make a lateral move is dependent upon so many factors. Sometimes you may really love a certain practice area, but your firm is not a real player in that particular area. Other times, you may find that you are constantly working with a partner with whom you do not get along and you do not see any end in sight.
If a candidate wants to make a move, and there can be hundreds of reasons for wanting to move, there are lots of positions available. The only way to really know whether a move is possible is by starting a search and sending out your resume.