Everyone that stated that Kenpachi's zanpaku-to is released is correct. Kenpachi's zanpaku-to is indeed permanently in Shikai. Arguing otherwise is meaningless because it even says so in the series.
You do not necessarily need to know the name of your zanpaku-to to release your sword. but you do need to know the name if you want to advance it's powers further.
Ichigo's zanpaku-to is also permanently in it's Shikai. When arguing about it's shape, one must consider the following:
- The zanpaku-to that Ichigo had at the start of the series was essentially a variant of Rukia's original zanpaku-to. It wasn't an exact duplicate. It had it's own personal features that differed from Rukia's zanpaku-to aside from it's immense size.
- When Byakuya destroyed Ichigo's ability to become a Shinigami, Ichigo underwent training with Urahara. The results of the training was Ichigo regaining his powers as well as obtaining the true shape of his own zanpaku-to.
- Ichigo has an unnaturally large amount of reiatsu. Just like Kenpachi. The two of them have more reiatsu than most Shinigami. Even other Captains. Ichigo once queried with Yoruichi about the shape of his zanpaku-to. It was during Ichigo's bankai training. Yoruichi was explaining the difference between shikai and bankai. Yoruichi commented that because of Ichigo's reiatsu, his zanpaku-to will always be stuck on shikai. Ichigo then commented that it was just like Kenpachi.
In conclusion, Kenpachi is permanently in Shikai. Ichigo is permanently in Shikai. The end.