Re: A few comments
"It seems a little peculiar that they were quite happy to use the charge on an electron to define the Coulomb, but didn't wan't to use the mass on the electron to define the kg (it is known to an appropriate precision)."
Except the rest mass of an electron is calculated from the Planck constant (and the Rydberg constant): any uncertainty in its measurement comes from the Planck constant, so you could say this is closer to the source.
"There is still a bit of awkwardness with certain units, like the definition of the second is based upon being measured at sea level (as general relativity plays a role)."
Took a bit of reading to figure out what's involved (time dilation caused by the differing scalar speeds at differing altitudes). I guess in the end you have to pick something because there are no real absolute points of reference in the universe.
"Also I will kind of miss Avagadro's constant being the number of atoms in 12 grams of carbon 12."
Probably because that would have to depend on the definition of the gram (or in this case, the kilogram). That puzzles me. Why does SI use the kilogram instead of the base gram? Might this change in future now that the standard-bearer has changed as well?