Yeah, once more Pokémon become available, I'm interested in making a Fire-type team, but it needs some Pokémon that aren't yet available in Generation VIII. I've already made a Normal-type one.Me too. I like to make Monotype teams to try out online after the post game. SwSh made this more fun with the Type coded stadiums and uniforms. Recently I’ve done entire play throughs of just one Type which is a big departure for me as someone who obsesses over no repeating types when I build a team.
I have also been brainstorming other themes since at least Generation II, but there weren't really enough Pokémon to get them fleshed out yet. The most notable one, though was a team themed on science and technology around Generation V, which Colress eventually would have, albeit missing a couple of slots (his team containing Klinklang, Beheeyem, Metagross, and Porygon2/Porygon-Z).
Most recent theme team idea I had is Pokémon themed on African safari animals. Currently, much of it is off-limits this generation too: I can't use Pyroar, Girafarig, or Zebstrika right now.