I can totally understand your way of thinking @Arenith. Big thinkers come to big solutions and subsequently to great sounds…!
However @kcleveland123 has a point. Air, specifically “free” air has a lot of parameters that can negatively influence the dielectric, most of all moisture. It is not for nothing that big and renown cap manufacturers go to great lengths to find all sorts of dielectrics, like honey, oil, heck maybe even peanut butter.
I don’t know if you are familiar with this character, who has a maybe even weirder hobby than we have: he “listens” to capacitors and has made a comprehensive list so important to me that I even take it with me when I go to bed. Maybe that’ll help you in your quest to ultimacy…
http://www.humblehomemadehifi.com/Cap.html
This Duelund is part of a LR2 538Hz high pass filter for my ribbons. Quite an investment, but very worth while I might add.
Here’s the result… https://youtu.be/crRviuQ-MXc