It appears that Mighty No.9 will officially be delayed till 2016 in an upcoming announcement at Gamescom 2015. A post on NeoGaf, quoting a post from the official Mighty No.9 backer only board suggests the delays are due to bugs in the online features the game has to offer.  Here is an excerpt from the post:

Of course, it is important to explain why exactly the game is being delayed.
As we have communicated in the updates to our backers, all of the core content for the game is developed and in a complete state.
However, there are still bugs and issues pertaining to the online features that are included in the game. These bugs and issues
have a direct affect on enjoyment of the game, so a decision was made to work these issues out before release.

While no actual release date is given the post does go on to say they are shooting for a Q1 2016 release.

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