Is it tough? There are only seven fundamental units. https://en.wikipedia.org/wiki/SI_base_unit

Just represent every unit in terms of them then it's good.

One problem with the array you came up is that the units are not orthogonal, since Joules = Newtons * Meters.

Will the Rust compiler ever understand numbers in types? I.e. will the numbers ever be more than just part of the string that is the type name? If not, then I don't know how possible powers will be. Maybe the solution would be to define some types for commonly-used powers, e.g. PowN4, PowN3, PowN2, PowN1, Pow2, Pow3, Pow4. Users who needed higher powers could define those types themselves, I guess.