Besides exploring the outside front street scene, I would say it might be cool to have a tv over the bar looping the trailer so players can watch how this whole thing started and at the same time, get educated on the unique features of the map so they can then go explore. Truly, I just don't know how you can make it any better - this already is a KF2 masterpiece.

A Beer mug with my name on it and helicopters .

Seriously though the one thing that if i could have anything would have been a trader shop at the dancefloor bar.. but i know and accept it would be out of place.
That was my first thought, but having given it a little more thought i would love a teleporter that was active during trader time that teleports you back to the dancefloor bar.
Also...
HELICOPTERS!!

Other than that nothing the map is perfect the way it is.

would it be possible to make an objective mode version of the map? something that encourages players to move around the whole map. fun objectives like bring skully a beer (carry something from bar to DJ booth), use all skateboards, use all planes, collect all guitars, etc.

Objective mode would be fun but I'm afraid I already reached the limit of the engine with the content of GrooveYard.
Engine limit is 500Mb per map, advised map size is 300Mb and GrooveYard size is 500Mb so I'm really picky in how I update the map not go go over that limit.
Objective Mode would need a lot of kismet work(programing) and I'm simply afraid it would take too much space for it to work ok.
I will try tho...

Okay, well that settles it then ... looks like Tisa is needing to create a whole new map for us .... hehe!

I love the map, it's awesome blew my mind. I wish the map was broken up into smaller bits. I wish i could just fight zeds on a tabletop, or in a bathroom all on its own. I love the scale of it all but it's a little overwhelming and slightly impractical. However, i eagerly await anymore maps you make, I love the giant scaling of things interesting environment to play in, never thought of it. Also the physics bomb, do you think you could make a map that is space themed, that has you fighting zeds in a low gravity setting. You're the best keep it up!

You kill enough zeds to make the dancing trader appear without getting the collectibles.