The roles in a ecosystem of one topic (e.g. sport bets) are described here.
However - Gnosis is meant to be a real platform and as such the general foundation for potentially very many skins.
Those could be: political forecasts (elections, legislations), news (terror attack), celebrities/gossip, music charts, movie revenues, future plot of tv-shows, weather forecast, features of the next apple presentation, economic data (unemployment rate, GDP, ...), predictions on court decisions, sport bets, scientific results and much more.
In principal all of this topics could be tackled by a traditional VC backed startup. However - there are more promising solutions coming up that might be far superior in building such sub-platforms/communities.
It is Backfeeds core idea to create an incentive and governing mechanism to let people contribute together to a common project. The core idea is that everyone can contribute to a group and might get rewarded with value tokens and voting rights by the existing group members.
One core achievement of backfeed is to have defined a protocol how to reward contribution that can not be easily valued by a formula or algorithm.
Taking about Gnosis: the task within one niche: creating propositions, resolving them, setting up market, ... can be rewarded by simple rules - for example based on the resulting volume/fees. However - for the process of setting up a new skin: building a proper frontend, defining the story, getting the first people involved,... - those tasks needs to evaluated by humans. And exactly here backfeed could help unfolding the full potential of Gnosis.
A new skin could start very small - even with one person. It might be nevertheless a good idea to start with a few subgroups - frontend, marketing, partnerships, ... If others would join they could earn tokens for their contributions. Those tokens can later be used as an additional fee to the gas costs to use this skin and therefore gain in value.