Oh yes, absolutely in favor of starting the year in the equinox (or at solstice). And while we are at it: change the days of a month to match the cycle of the moon - 28 days. So we would have 13 months. That's how they came to be: the earths rotation around itself is a day. The moons rotation around the earth is a month - and the earths rotation around the sun is a year.
But I believe, the natural rhytms are not perfect and constant, so I cannot claim, that this calendar would "never change from one year to the next". But I like the idea of directly refering to the natural cycles, instead of arbitary ones.
But like the other comment said, implementing any change of dates in reality won't be welcome, nor workfree ..
Interestingly the beginning of a lunar month is static (the new moon happens at the same moment everywhere on earth) while the beginning of a calendar month is sequential around the earth by timezone. The lunar cycle, earth orbital cycle (year) and earth rotational cycle (day) do not really sync up. There are approximately 12.37 lunar cycles per year (so once every 3ish years there is a 13th moon which roughly correlates to a "blue moon" although more specifically a blue moon is the second full moon in a given quarter. Each lunar cycle is not consistently the same length. That's just the tip of the iceberg. Source: I spent some time trying to mesh a lunisolar calendar model with our modern Gregorian model (https://www.cycalendars.com). I can't recommend lunisolar calendars as an efficient way of communicating consistent dates. Time becomes radial rather than sequential and integer timestamps cease to exist. But it is cool. :-)
The original Roman calendar was based on lunar-solar calendars, and they don't line up with a solar year, because a moon cycle is 29.5 days, not 28. The Jewish calendar is one such calendar. It's why Jewish holidays vary so much. Some Christian holidays are based around moon cycles, like Easter. All lunar-solar calendars get around this problem by adding an extra month every few years.
Well sort of. Christian holidays were originally based on the same cycle as the Jewish Holidays but then the church fathers didn't like having to go ask the nearest Rabbi when their holidays were and tried to do it algorithmicly with absolutely no consoltation with anyone that knew anything about time keeping or astronomy and invented the ecclesiastical equinox (always March 21), and ecclesiastical full moon, neither of which bares relation to any astronomical event.
But I believe, the natural rhytms are not perfect and constant, so I cannot claim, that this calendar would "never change from one year to the next". But I like the idea of directly refering to the natural cycles, instead of arbitary ones.
But like the other comment said, implementing any change of dates in reality won't be welcome, nor workfree ..