I think a good idea for a future month would be one where only all the Pokemon from one type can be used (e.g. all rock types). It would be a completely different type of metagame. For example, using the rock example, most Pokemon have high defense, so some Pokemon that are usually physical attackers would be better as special attackers in that metagame, and a Pokemon like Cradily would be probably a top tier threat due to it not being weak to Water and Ground, and Sandstream would raise the special defense of the whole tier, and so on.
Or in an all-grass metagame, it would be different too, with no spinners, and nobody would be able to use STAB moves, (moves like Sludge Bomb and HP Fire/Ice would probably be the main moves), Leech Seed doesn't work, likely rain/sun weather wars, and so on.
And lets not even start with an all-Dragon metagame, it would probably be one of the most offensive and fast-paced metagames ever.
I think mono-type metagames would certainly be interesting to play, even with randbats, if you ever run out of ideas lol.