I just did a head-count on the number of robots in each rumble (of only that weight class).
Which comes to this: 458 megabots 132 minibots 170 microbots 229 nanobots
I found that interesting, that there we're fewer mini and microbots then nanobots. Maybe a microbot (>250 + <750) only or minibot only (>750 + <1500) rumble would make those robots more interesting to develop.
Thats interesting indeed, the 'Do the best you can with the least possible code' paradigm is challenging to a lot of people. My vote for an extra rumble would go to 'ExtendsRobot', although I know the winner will be kawigi.robot.Girl. I am not sure if such a rumble is possible, because I don't know if it can be (automatically) detected which base class is used.
I noticed this a while ago.
I don't think that it's a very big deal. After all, the minirumble is for all robots that have a codesize of less than 1500 bytes, the microrumble is for all robots with a codesize less than 750 bytes, and the nanorumble is for all robots with a codesize less than 250 bytes. So, nanos and micros fit into the minirumble because, well, they are minis in the sense that they are all under 1500 bytes.
To say that minis and micros could could have their own exclusive rumbles would require different definitions of the weight classes. And, if you're going to all that trouble, you might consider more consistent brackets, like 250, 500, 1000, 2000.