Currently, we only allow members to suggest one niche per day. The reason for the limitation is that we wanted to prevent spamming and because the reputation engine is not in place yet.
Our plan though is to refine that model a bit for the beta.
One idea we had was to charge a small non refundable fee each time you make suggestion (approximately $5 in equivalent NRVE). However, if and when the niche is purchased at auction, you would receive 10% of the purchase price. Thus, you would come out ahead even if they paid the minimum, but you might come out way ahead if it sold for a premium. (In this model, the remaining 90% of the purchase price would go into the Network Rewards pool.)
The idea was to require users to have some skin in the game when making a suggestion, to encourage quality and thoughtfulness (and also reduce spam suggestions). In that model, there would be no need for a daily suggestion limit. After all, we want to increase the percentage of suggested niches that are approved and purchased. This model aligns all interests pretty well, in that regard.
The downside, of course, is that you'd have to pay to suggest, which would likely reduce the number of new niches being suggested.
Though I really like the economic incentives associated with this approach, I'm having second thoughts about whether it is worthwhile, especially if it makes niche suggestions less common.
Side note: once we have the reputation engine in place, we can more easily solve the spamming issue in general.
I'd be curious to hear your opinions on this concept.