I thought that I shouldn't just beat down other people's ideas without contributing my own, more stupid ideas, so here's:
The 512 grid size contest.
Rules:
-You must create, resize, cut and vertex edit all brushes using a grid size of 512.
-You may place and move point entities using any grid size.
-You must make your map for a gamemode which isn't MvM and doesn't require any server modifications or plugins to be run.
-You may not use the Transform window (Ctrl+M in default Hammer).
-You may not copy anything from any vmf other than the contest vmf, which must be empty prior to the contest starting.
-Concerning displacements, your paintbrushes (when painting geometry) must have a Distance which is a multiple of 256 (e.g 512, 256, 0, -256, -512) and a Radius of 1.
-You may not use props which are obvious conversions of brushwork made using a lower grid size than 512.
-In terms of surface area, brushwork should dominate your gameplay space. This is impossible to accurately measure and comes down to the judgement of the contest judges.
-For the sake of your sanity, you're allowed to use ABS prefabs, but not any other prefabs.
-Detailing using props is a waste of time since your map will not be directly judged based on its theme or the quality of its detailing, but rudimentary brushwork detailing can be useful if you feel that it helps to communicate your creativity and/or proficiency.
Inspired by someone saying "512 grid gang" in Discord a while ago. Maybe that someone was me, I don't know.
The contest would be a layout-only contest.
The contest should be judged based on the creativity and proficiency of mappers - trying to get around the contest's limitations by excessively using props would be something that would reduce your final score, for instance, as it's an uncreative way to approach the contest. Creating angled geometry would (probably) be something that would increase your final score, because it can be, if used well, an excellent demonstration of creativity and proficiency which jumps out at the contest judges and playtesters.
The contest should have a relatively short time frame, maybe 5 weeks, so that mappers are encouraged to work quickly and smartly with their restriction and creatively use all of their mapping skills to salvage TF2 gameplay out of their map, as opposed to giving in and making an overscaled mess. In order to not force contestants to realise this by themselves, the contest should provide information on basic techniques such as "You can use the clipping tool to create faces that are shorter than 512 units long and you can use vertex edit to easily edit brushes cut in this way", ideally in the form of a video tutorial.
Admittedly, I don't like how the average contest idea removes options from mappers, and this doesn't get around that, since it removes your basic ability to make geometry, which, though it requires thinking to get around, is a tad annoying at the end of the day. Other issues include - how do you stop mappers from accidentally reducing the grid size and working on a reduced grid size out of muscle memory? Even if they realise afterwards, stop themselves and delete the brush they made, it's still annoying to have to go through that process often.
Of course, if you think of any loopholes or basic problems that I didn't consider, be sure to leave a reply.