I remember a version of this that went up officially with pictures and stuff. What happened to it?

Yeah, sure thing! I love whenever someone makes a dynamic map/alternative gamemode. I'm surprised no one attempted a gamemode like this until now.
This map has been getting a lot of play time on my servers, I'm just not sure too many people know how to play it, heh.
I made it map of the week on my servers a while ago and put in tips for the message of the day, but I realized later I didn't even know how to play it properly. I might have to make it map of the week again at some point soon with proper tips/instructions. At least to give them awareness of the boss pool.

Wow thanks so much for the feedback, really appreciate it. I'll try to find some time to implement some of the suggestions, though some will be much harder than others. The spawn rng is outside of the maps control for the most part, there are some glitchy workarounds but the implementation is extremely tedious and may break things outside of certain gamemodes

I will say, from what I've played of it though, it's a pretty solid attempt at creating this gamemode. Pleasantly surprised, considering this is the first of any map like this (I was expecting it to be REALLY broken). The RNG can be pretty bad sometimes with the spawning though, but I'd love to see this as an official gamemode! (like TW suggested LOOOONG ago, heh)
I would think it wouldn't be too hard for TW to implement something like this on official maps, with just cutting out most sections of the map for a holdout style. Like they could have it on Nuked, where it's on the long stretch of straight street, with a barrier separating each team in the middle (their backs to each other). Or Burning Paris, they could separate the two teams with one being in the area with the truck/ambulance and the other team across the barriers with the area with one ambulance and the stairs/ramp leading down to the subway entrance by the bridge.Obviously, spawns would need to be balanced/altered.

Not sure if this would be possible, but if there's any way to limit really bad RNG (like 3 fleshpounds on one side), that'd be really helpful too.

One other thing I'd add is when the boss spawns, consider having some fairly thick pillars or columns come up (so you can take cover from Patty's chain gun/rockets or Han's gunfire). And maybe also have the barrier that separates the teams come down after a certain amount of time after the boss spawns (if possible). That way the losing team is forced to face the boss alone for a little bit (and a greater chance at dying), but if they survive after a certain amount of time, both teams can profit from killing the boss on Endless Mode.

I understand a lot of that is a BIG ask (and again, haven't played it enough to know that those would even be ideal suggestions), so just take it as that. Suggestions on limited experience.

Also, the value amounts for the other buttons I think should be a bit less (maybe 3/4ths of what they are). I think how proportionate they are to each other makes sense (Disable enemy trader > Lasers > Increased spawn rate, at least I think I have that right), but on at least a 7 wave game, you don't have much of an opportunity to use much of them. Especially when you have to decide between using one of the buttons to screw over the enemy team or donating to the boss pool.
Disabling enemy trader is probably fine where it's at though, considering how punishing that is.

Wow, I didn't know what each button did at first (I keep my healthbars at less than 50% size, so the writing was really small, so I didn't really notice it :P) and this map makes total sense now!

Haven't played it enough to offer too many suggestions, but I think the boss pool counter should be displayed if possible. Most people who play it have no idea the boss counter button even exists. I started donating to random buttons at first (although obviously it would've helped if I had noticed the writing on each button :P).
I think you should make the boss counter button stick out more from the rest. Like make it golden, taller, flashing or a giant button on the wall or something to that effect. Anything to make it hard to miss from the rest.

WHAT IS THIS MAP??!!

It works great and I love the lazers. The only thing I noticed is you can shoot and grenade through the blue door in the middle. It might be intended though either way good work.

Gonna try it out later. Sounds fun!

Thanks for testing, I expect it to break a lot so be prepared for frustrations; also be prepared for frequent updates

Major props for attempting to do this! I'll try it out on my server and see how it works some point soon.