Woohoo, a place to drop my crackhead gamemode ideas!
rd_reel (named for the action of "reeling your core in"):
Each team's core starts close to mid and easy enough to steal, but as they gain more points or contest some neutral objective their core physically moves further in their base, thus becoming hard to steal. The most fleshed-out and decent-sounding version of the idea was to name the core position closer to mid "A" and the core position further from mid and more in your base "B", have a neutral capture point and have it so that said point is easier to push than hold, your core moves from A to B when you capture it and moves from B to A (unless already at A) when the enemy team captures it. This would make it easier to steal enemy cores if they had less of a mid presence, which would make farming for points and camping all game much worse, because the enemy team could capture the control point, making it easier to steal all of your points. This means that it works better as a symmetrical mode because it facilitates a changing front line, and it solves the boredom of RD (and to an extent CTF, because this could be applied there, because RD is so similar) by making farming worse and making prolonged Engineer camping far harder. It also works differently to "KOTH with extra steps", because the points have to come from somewhere, so some farming has to go on, so teams have to choose between farming robots in their base or going for the enemy core, but if your farming strategy isn't as effective as the enemy team's because your teammates suck, you can go play around the point, which the enemy team isn't doing because they're using their effective farming strategy. You also have the added depth that owning the point doesn't necessarily mean stealing the enemy core - since both cores start at A and capping the point moves the enemy core to A, you could have an enemy team which attempts to hold A and farm, even if your team is playing around the point, turning it more into A/D than RD.
I should also mention that the ideal implementation for the moving point would not be two core locations which you enable and disable, but instead the core being on a moving platform which physically moves between A and B, so players who are on it aren't robbed by an event which occurred without their input.
sd_ (I haven't come up with a name yet):
This came to be as an idea about 3-4 months ago, when I thought "I want to make SD but it's good", and didn't stop thinking that until the present day.
There are three flags, all of which are neutral - one is close to your spawn, one is close to the enemy spawn and one is to the side of the delivery zone. This requires mirrored symmetry. I also made the adjustments of making it play to 5 captures and turning the delivery zone into a neutral control point which, upon being captured, spawns a func_capturezone for your team on it for 8 seconds, resets itself to neutral and locks itself for 20 seconds. If, somehow, you're interested in developing a map of this variety, I have a gamemode prefab I can upload, featuring logic for the control point, visuals and sounds as well as training annotations for every event. Though, I'm no HUD wizard, so I haven't made anything that can constantly track how many captures each team has, though you can kinda use the scoreboard for that, but players won't.
My vision for the gameplay is: Teams roll out to mid, whoever wins the mid fight gets to capture their flag and the enemy team's flag at least. The one who wins mid is less likely to have ownership over the neutral flag, since sending players to the neutral flag weakens your mid presence, so you don't win mid. This means that a team which captures mid is left with no flags and the enemy team owns the neutral flag and their own flag, while the team which capped mid has to wait for a respawning teammate or enemy to bring a flag to them, and has a hard limit of 20 seconds before they can cap again. This means that the team which first wins mid has 2/5 points and has to forward hold for ~30 seconds if they want to cap any flags at all, and if successful can cap 1-3 flags. This has the problem of requiring them to return to the point to capture, though. Then, if the team loses mid, the enemy team gets to capture at the very least their flag which they brought from their spawn. I predict that at this point, the score will commonly sit at 2-1, and the cycle begins to repeat. It's worth noting that any team can, at any time, go for the neutral flag to introduce some spice into this cycle, and it's easiest for a team trying to break a forward hold to try to do so. So, the neutral flag is a special comeback mechanic for a team that's losing (if used right), while it can also benefit a team that's winning if they're good enough to hold for a long enough time.
koth_ (again, no idea about the name):
Halloween map. Has an underworld, but the novel thing is that each team gets their own, always open, underworld (probably without constant damage) which enemy players can't access, and it has a boss in it. There are portals everywhere in the underworld which let you leave. When you kill your team's boss, your team gets full crits for 10 seconds or so, then the boss respawns. The boss could be anything really, so long as a suitable arena was made for it. You go to the underworld through a portal that's inside your spawn, and when you leave it you're teleported back inside your spawn. Right outside your spawn, there are powerups known as "sugar rushes" which give you brief minicrits and a brief speed boost. These mechanics allow you to choose between coop PvE or team-based PvP. The sugar rushes let you get to the point quickly and notably help against spawncamping - this is deliberate, since you might have a team where most players decide to go to the underworld when the enemy team's mainly playing in the overworld, so the enemy team steamrolls the point and starts to spawncamp you, so the sugar rushes help you to overthrow a spawncamp and reach the point on more even terms, while also allowing players to quickly transition between playing in the underworld and overworld, allowing them to use the crits they earn. The crits also help to break extremely heavy spawncamp situations. So, you can choose to play in the underworld or overworld, it isn't too affected by your team and doing one helps the other. However, I would want an extended KOTH timer, just so a team can hold the point and forward hold for a long time as they naturally would on such a map, without the other team being punished too hard for using the gimmick of the map. You would also want some portals to the underworld in the overworld just generally scattered about the map, so a team which mainly plays in the overworld can steamroll and capture the point, then go to the enemy spawn and realise that nobody's coming out, so they're all in the underworld, which is boring, so the overworld team needs a portal to the underworld (note that you could make overworld portals using two triggers, each of which is filtered to a different team, so either team can use any portal) so they can all leave the overworld and not have to try to spawncamp a team who isn't even there. This also opens up intense mindgames where teams wait for the entire enemy team to get bored and go to their underworld, then rush out of spawn and use the sugar rushes to get the advantage over the point. You might also want to have less ammo than your typical KOTH map would have and no sentry spots anywhere, so Engineers aren't encouraged to just set up on the point.
So, those are the crackhead ideas that I really like and want to make. Sorry that I wrote so much for all of them, I wanted to be comprehensive.
Funny how all 3 are "KOTH with extra steps".