Conceived together with the metric system, the French Revolution attempted to adopt a decimal subdivision of the day rather than the customary 24×60×60 system. It didn't catch on. And their units of more than 10 days still had to drop the decimal principle in order to align with the year.
The basic problem in calendar construction is that the most practical way to measure medium-length periods of time is number of day-night cycles they contain, whereas the most practical way to measure long periods of time is the number of seasonal cycles they contain. These two units are not nicely related by a power of ten; it's not even an integral ratio. Yet a system that doesn't respect both of these facts is doomed, at least as far as everyday use by humans living on Earth is concerned, so calendars in practical use will always be compromises.
For internal use in computer systems, it is common to measure time simply as a number of seconds with no greater units employed at all. In most cases this principle is not completely followed, though, because leap seconds are not counted, so what computer time really gives us is some approximation to the number of 86400ths-of-day-night-cycles, rather than the number of SI seconds.
(One notable exception to this is the time coordinate of GPS signals, which does count raw SI seconds and is drifting out of sync with civil time in discrete increments each time civil time introduces a leap second).
Some science fiction authors have speculated that future spacefaring civilizations whose life is not tied to the rotation and orbit of Earth might use SI multiples of the second instead of days and years (a megasecond is about 10 days, a gigasecond about three decades, and so on) -- for example, Vernor Vinge in A Deepness in the Sky. Even so, Vinge recognizes that people living on planets will want to use a calendar that makes sense of their local days and seasons. His culture of interstellar traders have a saying that you know it's time to move on when you start using the locals' calendar in casual conversation.