Well, we could always switch to another time unit that uses 1 day as the base unit. Then you would just use md, nd, Gd, Md and all the other prefixes to get to the scale you need. That would be fine for most purposes.
However, the problem is that a day isn’t exactly 86.4 ks, since orbits and rotations are wobbly and messy. If we define the day as a unit today, it won’t be the same a thousand years later. Perhaps the people of the future could use that for common purposes, but scientists would need to use a more precise version that has a crazy litany of decimals at the end. Using the Earth as a foundation for any kind of unit is just asking for trouble in the long run.