ask us devs on telegram https://t.me/plebbit or submit a pull request on https://github.com/plebbit/temporary-default-subplebbits. Sometime this year we will enable gasless voting for plebbit accounts holding PLEB, they will decide which community will enter the default feed on https://seedit.eth.limo/#/communities/vote by upvoting or downvoting them. So we won't need the centralized temporary list anymore. The same will be done to whitelist NFT collections I think.