Kim dotcom hasn't proposed investing. He has shown interest in being the biggest customer. The risk of investing in the cable is huge, there isn't a datacenter in NZ that can utilize the proposed bandwidth increase. This is essentially a chicken-or-the-egg situation where someone other than dotcom will be bearing the risk.

An article where the reporter actually spoke with DotCom: http://www.nbr.co.nz/opinion/dotcoms-cable-fact-or-fantasy-k...