Firstly all Niches that are approved should make a postive contribution to the platform and Ted has created a fair process to achieve this and its start with your idea!
Then you can input it into the approval process, you would in a effect suggest or nominate a new Niche into the system.
Then a 48 hr process will start where each community member who has a positive Reputation will get the chance to vote on that niche those with higher rep will have more impact but (for the Alpha I think this will be less a factor) but the vote will be ether up or down.
After the voting is done and based on a majority ie great than 50% it will either become a Niche channel or not.
The bidding process I believe is for 48 hours for a new niche, the max I understand a Narrator can own is up to 5 niches.
And if your suggested Niche is taken by another or you are out biding I think you would get some Kudos for suggesting the niche with a improvement in your Reputation. : ) but that does not stop you from trying to buy another Niche within the limits set.