A lot of points were made already, but Tyranitar was #1 on the usage stats as of September 2011 (not sure about months earlier than that, but I'm sure he was somewhere in the top 3). With the banning of Excadrill, the top abuser used alongside Tyranitar, there is definitely going to be a drop in usage. I don't think it will be that big, but it may drop him 5 or 6 spots. He is still effective for the purpose of just having weather, in order to get rid of rain or sun (or hail) that may be in play. He also has many different possible sets, like shadow_scyther pointed it, which makes him very unpredictable.
As for banning his ability, I don't think it is ban worthy. Excadrill was really the only big abuser. Banning Excadrill seems much more fitting than banning the ability as a whole. While there is still Landorus who can take advantage of Sand Stream, it is definitely not a big threat. Like dragonexpert said, with Rain and HP Ice being very common in the metagame, Landorus is not as big of a threat as it could be.
Terrakion is definitely a major player in the metagame which can benefit from Tyranitar's ability. Without repeating what dragonexpert said, he still has some big threats that can control it. Terrakion with a Sp. DEF boost is not something that should be taken lightly, but it definitely is not as powerful as Excadrill in a sandstorm.
My final opinion on if Tyranitar is centralizing the metagame is no, it is not. While he may be a force to reckon with, he still has a lot of threats to him. Gliscor is one of the most obvious ones that can check most Tyranitar, but Tyranitar can be unpredictable and carry Ice Beam for that. dragonexpert posted a lot of the major threats to Tyranitar and those are all viable checks to it. Rotom-W was #2 in the usage statistics of September, reason being is that it could effectively control the #1 most used Pokemon. With options like Will-o-wisp to cut its attack and Hydro Pump to actually inflict direct, super-effective STAB damage, while still having above average defenses on both ends. It can even utilize Pain Split which can keep it alive for even longer. Of course Rotom-W is not only used to check T-Tar, it is an all-around good Pokemon. But I think bringing up one of, if not it's biggest, counter is important when analyzing it.
I personally find the Special Defense oriented Tyranitar to work best for me. Now that Sand is a smaller threat, Sun teams are rising in usage slightly. Volcarona is a big threat to most of my teams and I find that Tyranitar can handle it very effectively. Specially Defensive Tyranitar can not only survive a +1 boosted Bug Buzz, but it can counter-kill with a 1HKO Stone Edge (provided that it actually hits, of course). If you prefer running something safer in terms of accuracy, Rock Slide also provides that 1HKO.
The set I'm talking about is:
Tyranitar @ Leftovers
Ability: Sand Stream
EVs: 252 HP / 4 ATK / 252 SP. DEF
Careful nature (+SDef, -SAtk)
- Stealth Rock / Pursuit
- Crunch
- Stone Edge / Rock Slide
- Superpower
While this may not exactly be a creative or new set, I feel like it's overlooked. Stealth Rock is not a must, if you have another Stealth Rock set-up on your team that you prefer. In that case, you can use Pursuit over it. Superpower is for handling mostly other Tyranitars, but in most cases it won't be outspeeding them so it would need to be crippled or on a switch-in. Superpower can also hit Terrakion on a switch-in or if Terrakion is paralyzed or crippled in some way, and can hit Ferrothorn for a FAIR amount of damage. In general, Superpower is to cover against the Steel types that Rock + Dark fails to cover. And like I said before, it is able to take out Volcarona very effectively.
I like this idea and I think it can bring some good activity to the competitive forums.