absolute motherfucking barrels of fun. I'll do the site if needed. 

Sounds like a cross between King of the Hill and Jailbreak :)

To make things more interesting, you could have the following:

func_doomsday - the ent that actually kills all the players. Must be triggered. Has built-in counter.

trigger_doomsday - brush trigger which must be constantly fired for a set time: i.e. the player doing the triggering must remain in the trigger field, alive, for that time. Death resets the trigger. Someone else entering the field resets the trigger. For evil grinnage, give it an angle to force the player to "operate" the controls.

func_doomsday_button - brush model used to target a func_doomsday. There may be several of these. The idea being that the would-be doomsdayer has to run around getting all the systems up, and hoping nobody comes after him and starts resetting anything. Whoever trips the most switches needed to fire the device gets the doomsday frags. End result: player can't stay in one place. (If each switch is triggered by a different player, the device resets itself and awards a frag to the 'defuser'.)

In other words, the concept as originally explained has all the players converging on one spot or trying to; I like to think my idea offers some more flexibility. 

nt 

the cool thing would be:
if the doomsday device takes a while, like say 15 seconds, then the other three players are now essentially on the same team, so it becomes 3 vs 1, and that would change in a split second as soon as the 1 guy setting off the bomb is dead. :D

it would be cool to make the trigger duration mapper changeable, so that different maps can have different times for the bomb to be set up (and go off)

i'd play it 

At this point, you may be thinking, "so all I have to do is resist the urge to add a Doomsday Device to Quake?".

http://www.planetquake.com/expert/GameDesign.html#xExampleDoomsday 

That's what I had in mind. 

I immediately remembered that article too...

: ) 

and a powerful long range sniper rifle

... why does anybody think that's a good idea...? 

sniper rifle in Quake, NO!!!!!!!!!!!!! :D 

force of habit, I think. Oh, and 'rheallisisim' o_O 

The bottom line on Doomsday Devices is that they create a way to score points without requiring as much skill as other means of scoring points, which is a gameplay problem that can occur with much less extreme and less easily recognizable analogs of the Doomsday Device, such as a powerup that is easily acquired.

well, that's not exactly what was broached, because it would take skill to set off the bomb. the idea is that it's not simply hitting one button to set it off, it's sticking around, defending the bomb from others killing you for a specified amount of time before it goes off and you score points.
that article is assuming a bomb would be a simple onehit trigger thing.

also, fuck sniper rifle, put in a stake gun! massive damage, slow firing and gravity affected! :P 

One thing in that article which I think relates to the suggested mod is map familiarity. Because the location of the DDD ( semi-cool abbreviation (c) Kell McDOnald 2004 ) is map-based, not player-based then the complexity of the map being played, in terms of connectivity anyway, probably has more influence on the outcome of the match than itemload/placement or player skills/styles. Even a map with lots of possible routes or opportunities for trickjumps will go stale faster than a map for conventional gametypes.
Yes, in CTF the flags are placed by the mapper, in fairly predictable locations and always spawn there. But flags can move. If they're carried. Having played a brain load of Q3CTF online, I can say with absolute certainty that the most interesting eventuality to occur in CTF is when both teams have possession of the flag. Knowing the location of the flag spawn is then more or less redundant.

Still, even predicting something of a shorter lifespan of enjoyment, this mod would be fun. For a while. 

It would be fun for a while, but it's heavily dependent on map designs being fresh. Once the maps get boring, the mod will, too. 

weapon_doomsday - The Doomsday Device.
1. Find the Device
2. Pick up the Device, which starts the timer
3. Run around trying to avoid getting shot before it goes off

If the user does get killed, the weapon is dropped (duh) and its timer resets. The operator cannot use powerups (i.e. pent, quad, ring) or weapons while holding the device (hey, it's a weapon.) (Armour and health are OK though.)

Actually, such a device would be a lot easier to code than all these funcs and triggers. All you'd need is a couple of models. And it's a lot more like Catch the Chicken now... 

You guys remember DemonTag?
that was a fun mod 

Catch the Chicken. One of my all time favourite mods. Incredibly simple and tremendous fun.

And it's doesn't require a lot of special mapping.

If FPS games are, as some suggest (and far more deny), destined to be the new spectator sport then this mod should be the thing that's contested. Not 1on1 but FFA and TeamChicken. I'd subscribe. 

All you'd need is a couple of models.

map model - http://kell.vondur.net/doomsday/ss-doomsday-1.jpg
view model - http://kell.vondur.net/doomsday/ss-doomsday-2.jpg
download - http://kell.vondur.net/doomsday/doomsday-model.zip

The zip contains both versions of the model plus a wad with a few spawnmarker textures for making a pad like the one in the screenshots.

You may find this useful. 

First, one spawnpoint, or random choice of several?

(The reason for asking is that if the item_doomsday only appears in one place, it might boil down to map knowledge again.)

Second, if the bomb carrier is killed, should he just throw the bomb? (If the bomb lands in lava or a killpit, I was thinking of having it warp back to the spawn.)

Third - how should the bomb carrier be identified? A bomb model over his head, like a Holy Wars halo? A constant beeping countdown emanating from the bomb (being a directional cue)? A glowing effect?

Fourthly, teamplay? 

Second, if the bomb carrier is killed, should he just throw the bomb?

As you mentioned, be careful of having it get thrown into a hard-to-reach location. However, also have it go back to a spawn location after x seconds. 

I was thinking more along the lines of having a sort of dynamite detonator which you would have to stand on. If noone is on it it would rise twice as fast as it sunk when someone stood on it. So you can go off and still continue later, basically, who ever is standing on the detonator when it goes off gets the points.

You know a detonator, like in all the cartoons, with a t-shaped handle on top of a box? If its teamplay you would have to protect your rather exposed detonator dude. Takes about 15 seconds of uninterrupted standing to make it explode? 

Still haven't located an edit function, I just wanted to add that this is my opinion and simply ignore these 2 posts if you do not find it good or appealing.