Defensive End:
Moving Forward: As the Texans transition to a 3-4, they will be very happy to have Antonio Smith and Mario Williams as their DEs. The 3-4 DEs have to be tall, with strength and long arms and that is exactly what Mario and Antonio have. 3-4 DEs are more about power and bull-rushing than finesse and "moves" so in that regard, I really like those guys at that DE spot. Barwin will be able to fit in as a 3-4 OLB and a DE when they go to a 4-3 hybrid look. Barwin will probably be best suited as the weak-side OLB on the QBs blind side. Many times, this player will rush the passer more with less coverage responsibilities. Mark Anderson probably isn't a fit any longer in the 3-4, but Jesse Nading might be able to compete for a spot as a 3-4 OLB.
Defensive Tackle:
Moving forward: Cody has the size to be a rotation player at DE or NT, but he's not really suited for those positions full-time. Still, he'll be on the team next year. I could see Earl Mitchell as a rotation player at the nose, but he's not big enough to be a full-time 3-4 nose. Mitchell is quick off the snap and does have some strength so Wade Phillips could probably make use of him. Okoye's short arms and lack of strength at the point of attack mean he probably can't play the nose and he does have the size or length to play the DE spot. My guess is that the Texans will try and trade him unless they feel like they need him to fill a roster spot out. Any way that you look at it, the Texans don't have a classic 3-4 nose on the roster and they will have to draft at least one while searching another out via free agency.
Cornerback:
Moving forward: I feel very comfortable saying that Antuan Molden is gone and it is pretty likely that Brice McCain will be gone as well. I fully expect the Texans to bring in a veteran CB like Ike Taylor or Champ Bailey to be a starter while letting Kareem Jackson fight for the 2nd or 3rd CB spot. I said it before and after he was drafted and I'll say it once again - Glover Quin needs to move to one of the safety positions. While Quin isn't as fluid as you would like turning and running as a corner, he would be an above average safety in terms of coverage and he's tough enough to play either spot in Wade Phillips' defense. By moving Quin to a safety spot, you take care of a position that you've struggled to fill since the inception of your franchise and it would free the Texans to concentrate on drafting another CB in the first three rounds. Jason Allen will probably make the team next year.
Safety:
Moving forward: There will be some people who will wonder out loud if Pollard can play 3-4 OLB and the answer is no. He can, however, play that position in certain exotic packages, but not as a full-time OLB. I do not think it is a lock that Pollard is back. As Wade Phillips knows, box safeties (see Roy Williams) can get you in trouble pretty quickly on the back end of your coverage. Wilson will probably be gone if the Texans bring in a veteran safety or move Quin to safety, but Nolan is likely to get one more year to prove himself because he's young and cheap. As for Dominique Barber, the team has always seemed to like him when he's healthy so my guess is that he's safe next year. This might finally be the year the Texans draft a safety within the top three rounds.
Linebacker:
Moving forward: The first thing the Texans need is for DeMeco Ryans to come back with the same mobility he showed before his achilles injury. If he does that, he'll be a nice fit inside in the 3-4. I know that most people believe Brian Cushing will be a good fit as an OLB in the 3-4, but I'm not so sure I agree. Cushing can play the position, but I don't think he has the edge speed that you want from the position. Instead, I think Cushing is better-suited to play the ILB position where he can thump and the Texans can use him as an effective blitzer inside. I'm sure the Texans could still put together packages that allowed him to rush the passer from the OLB spot from time to time if necessary. Sharpton could be in some trouble trying to make it in this defense over the long haul. He doesn't have the size or physicality that most 3-4 defenses want inside and I doubt he can play outside. Diles might be able to compete for a backup role inside. The Texans definitely need to find an OLB with a presence off the edge either in free agency or the draft and it needs to be one of their top priorities.
Kicker:
Moving forward: I'm sure the Texans would like to have a kicker with more leg than Rackers, but the question is whether or not Kubiak will have the stones to rely on a rookie kicker via the late rounds of the draft. My guess is that the Texans will bring in competition for Rackers but they probably won't spend a draft pick on one.