Teslas do this, they show battery charge in terms of miles or kilometers which is obviously not the correct unit. It's more abstract and often wrong but closer to what the person wants to know.
Oddly enough the iPhone doesn't do this, it will happily tell you how many GB you have left when what the user really wants to know is "How many more songs or photos can I store?".
I actually think that what Teslas do is good. It is the most accurate representation of driving capacity. And a lot of non electric cars are doing that now too.
The first few years of bluetooth headphones would just give you an alarm when they were at 5% capacity, and that was it. And in general, there is very little feedback given about what your storage is doing and where it is located. Just a simple question of "where are your photos" can be hard for most people to answer now. "Uhh, the 'eye cloud', but also on my phone. I mean some of them are and some aren't."
And that is why people are constantly losing their data now. I have seen plenty of people hold onto their old phones because they have data that they don't know how to get off, and it is just easier to hold onto the entire device.
when what the user really wants to know is "How many more songs or photos can I store?"
That depends on how large they are, and that can vary widely, which is why abstracting away files (or more specifically, file size) is such a bad idea.
How many KM remaining depends on the terrain, traffic, driving technique, weather and a host of other factors. Nobody is expecting 100% accuracy just a rough estimate. They are already mentally doing the conversion anyways.
Oddly enough the iPhone doesn't do this, it will happily tell you how many GB you have left when what the user really wants to know is "How many more songs or photos can I store?".