Clean out or future vent?

Hi from Calgary,

The first basement image shows what I think is a future vent with a plug on the left, and at right is the kitchen drain stack to basement. The second main floor image is directly above the first picture and shows that same vent pipe elbowed into the wall. At right is the kitchen drain stack, trap arm and the vent above that also goes into the wall. There are no other second floor plumbing fixtures above these.

Is this a future vent or a cleanout? I am not sure why they would need a cleanout there, so I think its a vent that meets up with the kitchen vent inside the wall. I need to tie into a vent for my basement bathroom. I am planning to verify with an endoscope camera but I can't get the damned thing to work.

For some reason I could not spin the plug out so I cut it off with the intention to tie into it or cap it again. It was full of water, which one would expect given it is a low point in the vent system (I think).

Thanks.

James