Will Coby be relevant?

[SSJ2]

He now has Haki, a trait every Vice Admiral has. Do you think he will play any sort of role later on?

 

[Uchiha]

Yup, in the final war for sure. The question is whether Smoker will be the next Garp or Coby.

 

[SSJ2]

I just don't see him making it up the ranks too far if Akainu is there. I think Smoker gets the big promotion, and Coby might get stuck at Vice Admiral level.

 

[Yoshi]

Yes, absolutely. He wouldn't be introduced in the beginning of the series as the world government counterpart of Luffy for nothing.

 

[Papasmurf]

Smoker sucks too much and is rather old to be Luffy's navy rival

 

[SSJ2]

I just don't see his path to power. Akainu was about to kill him in the war after all.

 

[sei'taer]

Coby's path to power probably exists after the great war. He seems a shoe in for the face of the navy at the end of the series.

Plus it's his dream

 

[Symbiote]

Coby's path to power probably exists after the great war. He seems a shoe in for the face of the navy at the end of the series.

Plus it's his dream

Dreams do play a big part in this series.

 

[Captain Cadaver]

I just don't see him making it up the ranks too far if Akainu is there. I think Smoker gets the big promotion, and Coby might get stuck at Vice Admiral level.

I highly doubt Smoker will become an Admiral with Sakazuki in charge. Smoker has shown some distrust in some aspects of the Marine's security, mainly in Punk Hazard, so it's doubtful he'd entirely comply with Sakazuki's regime. He was also shown to be somewhat close to Kuzan post-Marineford, meaning his views on justice may mirror Aokiji's. Smoker may very well leave the Marines at some point, honestly.

As for Coby, it's worth noting that Oda stated in the promotional guide for Film Z that Coby's Haki has become far more advanced post-timeskip, which was demonstrated in the Episode of Luffy special along with his Rokushiki improvement in which he shattered quite a large metal disk and used Ranyaku with his arms. He was also promoted to Captain and whilst the special isn't canon, Oda has stated that most of the things the anime staff do need his permission, meaning they probably wouldn't have added those details if the manga were to contradict them.

They're not exactly huge feats by New World standards, but they present a good grasp of Coby's growth.