>>4260339>with a speedbooster it can be doneIt can be and is done just by designing a native lens. Consider the "speedbooster" just part of the optical design. Lenses already correct the light path multiple times to get it to your sensor with opposing convex element groups.
Make the elements large enough and you can gather as much light as you want for any focal length. The reason it isn't done (other than practicability and money) you already stated: it would look awful without a ton of expensive glass getting it to your sensor properly, and depending on what you want be anywhere from 100 pounds to several tons.
There's also the market... who would need this? There's only so much available light in very low light situations to the point that exposing film by unspooling it in your hand will barely do anything, and high speed photography uses flashes. It just isn't a priority after a certain point.
