Portal 2 Co-op Vehicle
That way you dont have to worry about landing upside down or traveling sideways through a portal.
Also this would be much more precise to handle in physics puzzles where the chamber reacts to the vehicle.
Another advantage of a spherical vehicle is that it wouldn't "clip" through the portal edges and look ugly. (like putting a cube halfway through a portal that is at ground level)
The layout could be similar to how violet and dashiell in the Incredibles movie manage to run around in that forcefield sphere.
Though now there would be one person "driving" the ball, and another one shooting bigger portals.
With the hamsterball, you could also add some animated gimbal construction to keep the seats/mounted portalgun orientation level while the outside sphere is rotating around.
I guess that if the vehicle had a diametre of just under 128 units, and the "vehicle portals" being able to fit onto a 128x196 slab, you could create some awesome puzzles with that.
Having a 120x120x120 sized ball would also still maintain the current scale of all the test chambers, no need to acomodate a monstertruck.
A last advantage would be, because it is such a unusual shape for a vehicle, you could design something completely aperture sciencefiction styled.
MissStabby just blew my mind. I think I could actually visualize this Hamster Ball Portal Device.
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haha, glad to have blown your mind 
How about getting together a small mod team to create the ASHBPD into a working element?
(FYI i cant program, though i can do 3d art and portal mapping)
Also since "vehicles" aren't supported in portal2, what if at the start of the level, both cores of Pbody and Atlas are just "inserted" into the vehicle, and the game actually just handles it like the vehicle is not a vehicle but a oversized playermodel. The First player would have freedom of movement (even though it is heavly tweaked, and linked to some spherical physics body) and the second player would be in charge of the mounted portaldevice, but unable to move the sphere itself.
You could even have the playermodel of atlas be the entire vehicle but without Pbody's core (since he's the one that can see his playermodel. And have Pbody be the entire vehicle but without Atlas's core.
The only problem would be that because you can see yourself through a portal, you would have to disable that in some way, else you can see 2 models ontop of eachother. Another thing would be that if there are animations involved they would need to sync up between both players on a single viewmodel.
Also i think "thirdperson" view of the vehicle would have to be something for lateron, since getting it to work as a playermodel would be quite difficult as a start already.
For the transition between the vehicle and running around, you could get away with some "disassembly/reassembly docking stations" (and adding a level load to it aswell) as leaving the vehicle on the fly would make creating puzzles a lot more difficult.
Another "benefit" to adding just the cores of the 2 bots would be that you could even try to create a very small "vehicle", like 60x60x60, that way you dont need to modify portalsizes, you can operate buttons, ride excursionfunnels, hard light bridges and you can even get transported via the diversity vent systems.
A nice explanation of the situation would be that glados finally managed to convince the reassembly robot to mix up stuff a bit, to see if the bots were capable of solving the puzzle without arms and legs!
These Vehicle puzzles could actually be more focussed on quick thinking and shooting portals while at speed, since one player is purely occupied with driving and another with popping portals.
Also new obstacles would need to be overcome, since you cant lift objects and are contantly carrying around momentum, so you could end up drowning in goo a lot quicker.
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hmm... this is getting interesting. Also since this is a vehicle we're talking about, it should move faster than a player's regular moving speed.
My Work
[spoiler]Maps:
Revenge of the Angry Turrets
Capture the Cube [Co-op]
Capture the Cube 2 [Co-op]
TPWEGTH Sample Map
Aperture Aquatic Testing Center
Aperture Aquatic Testing Center 2
Aperture Time Testing Center
ML's Halloween Trick - 1000 downloads!
ML's Halloween Treat
ML's Combination - 1000 downloads!
ML's Jailbreak Labyrinth
ML's Tricky Teamwork [Co-op]
WIP:
"Capture the Cube 3"
Workshop Maps Link: http://steamcommunity.com/profiles/76561198008890579/myworkshopfiles/[/spoiler]
If you have played the Glados levels in The Ball, you already know how that hamster ball vehicle idea would work out. Also this:
Back to the Future! I think I have watched too many movies over the years.
VDC User PageA hoverboard huh?
My Work
[spoiler]Maps:
Revenge of the Angry Turrets
Capture the Cube [Co-op]
Capture the Cube 2 [Co-op]
TPWEGTH Sample Map
Aperture Aquatic Testing Center
Aperture Aquatic Testing Center 2
Aperture Time Testing Center
ML's Halloween Trick - 1000 downloads!
ML's Halloween Treat
ML's Combination - 1000 downloads!
ML's Jailbreak Labyrinth
ML's Tricky Teamwork [Co-op]
WIP:
"Capture the Cube 3"
Workshop Maps Link: http://steamcommunity.com/profiles/76561198008890579/myworkshopfiles/[/spoiler]
Couldn't it be as simple as giving the partner a piggy back and racing down some propolsion gell ? With the piggy back, it would prevent using the portal gun useless while being ridden but needing to control which way your going.