Troops are one of the areas that I feel need a lot of improvement in a new codex. Here are my thoughts, piece by piece. Overall, the biggest problem Tyranids have with troops is they need a way to claim objectives without a Synapse babysitter. Genestealers are the only troop that can do this, but they are needed as assault specialists, not campers.
Overall, I think 'nids are still a strong codex and fun to play. These wishlists are simply what I'd like to see fixed or improved in a new codex.
Genestealers: Our most deadly troop unit. However, with the nerf to rending I feel they are somewhat overpriced, especially once you give them extended carapace and flesh hooks. I'd like to see them drop in points a little bit. Other than that the only thing they really need is for Flesh Hooks to not be a "head" upgrade. Currently, they can't take any of the other upgrades ever because Flesh Hooks are so necessary. Imagine if a Marine Assault squad had to choose between giving them all grenades or giving the Sgt. a powerfist. I'd like to see the hooks as a chest upgrade so we can see more variety in 'stealers.
Furthermore, I predict that Stealers will be moved to Elites, and that taking a Broodlord will unlock them as a Troops choice.
Gaunts: Fluffwise, our most numerous critters. However, compared to Ork Boyz they are extremely overpriced. Either their price needs to drop (or Orks need to have a points increase), or they should be given "Without Number" for free. Also, I would really like to see biomorphs like the Strangleweb and the Spike Rifle come back. It would be fun to see those old Brood mutations return. The Strangleweb could be basically a flamer but perhaps use Initiative instead of Toughness to determine wounds, and the Spike rifle could be a low AP weapon since Tyranids have nothing better than AP 4 (I'll go into the weapons and biomorphs in another post).
Hormagaunts: These guys need to be cheaper. As is, they're not terribly effective as assault troops, and they're too expensive to be meat shields. Also, they need to lose the "beast" designation since it means they can't attack upstairs (nor can they deepstrike in Planetstrike).
Rippers: So useless in 5th. They're so useless that you get them free with other models. They can't take objectives, and get destroyed so easily. To make them useful I'd like to see them get an ability to "consume" an objective. This would be done in the assault phase and they would either destroy the objective so no one can get it (perhaps not) or they would form a protective shell around it, increasing their toughness/wounds/armor and holding the objective until killed. This could make them useful again, and remove the need for a Synapse babysitter to claim objectives.