Nostr is good for real world relationships because you see who you follow without getting burried by an algorithm. However, it is very text focused. Facebook grew by using games, then once you had built a network of friends you could see what your friends were posting. This overcame the chicken and egg scenario with building a social network. 

A daily challenge game like sukudu or wordle where you can see your friends score would be great. It could be embedded into websites like the NY Times have done to wordle, but because it's nostr the same game could be played on different sites or dedicated apps and you could see the results of all your friends, wherever they played the game. This could easily get a greater network effects than wordle. Every site that's not NY Times has an incentive to get on board to offer something that doesn't take people to their competition.