The 49ers defense is in an interesting predicament this year. They are faced with the situation of an defensive line that has two new players on it, and one that is aging quickly. The only safe person is Bryant Young, who was injured for a bit last season. They are also short at LB and DB. However the defensive backfield is not a factor in deciding the appropriate scheme. The 49ers are now at a fork in the road. There are two ways that they can continue on.
The first option is to continue on with a 4,3 defense, and hope that there defensive line holds up. This process will likely involve drafting a LB who can be converted into a defensive lineman.
The advantages to this is simple. The expression don't mess with success, is key here. The 49ers for years have been featuring a 4,3 defense, and have been quite successful with; especially over the last few years. Lastly stuffing the run wont be an issue, but if they switched to three defensive line men, they may be susceptible to the run.
The second route that can be taken is featuring a new look. A 3, 4 defense. This would involve re-writing the defensive play book. It would also involve drafting two speedy linebackers who could step in. One immediately and another maybe next year or the year after.
If the 49ers were to sport this new look, there would be some advanatageous points. For starters a new defensive play book, would mean that the 49ers would have to modernize their defense. This is key in beating the opponents to the punch. Bill Walsh did this by re-writing the offense, why can't it be done on defense. It would improve team speed, because the defense would have to move quicker. This would insure that the offense of other teams would not be able to run long plays, because the defense is so quick. Lastly the new look would disrupt offensive coordinators who are used to a four, three defense.
It's a toss up. Either way the 49ers choose to turn, no matter which path they elect to take, the end result should be the same. A faster, defense that remains near the top every year. The 3,4 defense seems to be the way of the future though, and I wouldn't be surprised to see the 49ers start to switch over soon. The Packers are also considering a switch, however their switch would be of necessity rather than desire.