I like the idea of basing everything off fractions of the speed of light, but still keeping base ten. Define 1 year as the time it takes for Earth to go around the sun(somewhat arbitrary in that its human centric, but the alternative seems to be defining it based off an arbitrary phenomena or an arbitrary factor of the planc length). Define 1 month as one tenth of that, and so forth. Admittedly our days wont line up with the day night cycle, but who needs that? Days are arbitrary anyways, and only matter to ensure your factory workers show up as soon as theyre legally allowed to.