Should I accoustic treat it, light it, and shoot videos against the concrete walls as a backdrop? If so, what videos?
Yes, you should. For practical reasons, you’d want to avoid videos that utilize lab equipment. Therefore, the most obvious videos to shoot there would be mailbag videos. When there’s a teardown segment within, those parts could be shot upstairs, but the majority could be handled in the bunker.
I suppose if you got a hot plate, you could also start doing introductory cooking videos down there where you simply dumped cans of things into pots.
Mailbag? He went to a lot of effort to put a giant TV behind him for mailbag videos so they would not be the best choice. Before that it was corner or no corner. And, it might be everyone's favourite video but there's still only been three this year by my count. I'd pick some other type of video.
The only reasons I can see to get excited about shooting videos in the bunker would be to either avoid moving the heavy stuff or to classify use of the bunker as a tax deduction.
Even the post apocalyptic inventor doesn't worry about backgrounds that look cool. Repairing societies junk is cool. Trying to look cool is ironically not actually cool.
If I look through the list of channels I subscribe to only a few have ever mentioned the background. Mostly It seems to be the precursor of a relevance bypass operation when the background becomes the focus of interest.