> jan 1st each year is an uncounted bonus day

This is the problem. There will be drift across years.

Ignore months for a bit. The length of a day is not a perfect multiple of a year.. of course, they're independent phenomena. The fact that a year is approximately 365.24 days means we can roughly correlate them with 3 365 day years and 1 366 day year, with the next exception happening in 2100.

But, even ignoring religious significance, so much regarding employment, planning, and pop culture relies on every 7th day resetting the cycle. There's no reason to construct a "new" calendar that messes up that pattern. If there was to be an alternate calendar, it should just tick upwards independently of the concept of weeks or months. Something like today is "Day 8431" of the 3rd millenium. And use kilodays, hectodays, and decadays. Weird, but so is every other alternate calendar concept. At least this one would make time keeping off-Earth simple.