I'm for this idea. Large sports communities could bring multiple new instances and also just a flood of active users in other communities. If we were to pick a specific community to come join, these guys and people in tech communities should be the first choices.
Communities centered around sports teams like r/chelseafc or r/lakers could warrant an entire Lemmy or Kbin instance with separate communities about that particular team (trade/signing rumors, live games, social media posts, etc). For them, federation actually has some huge benefits.
Plus as a side note, I'd love to have the regular diehard sports bickering on the Fediverse. Seriously. They'll be quite the counter to the current culture of the Fediverse, however. Arguing about Mbappé's longevity or whether the current NBA champions will win again would drown out the politics anyway, which is a massive plus in my book.