As for the UNIX Epoch, since less than six percent of computers worldwide use UNIX that might be the wrong choice. OS market share Microsoft Windows machines (93% market share) use January 1, 1900 as zero. Also arbitrary, but just as valid and requires fewer people to do anything than the UNIX-based date.

Notable atheists in the past have used the the date of the execution of Giordano Bruno to adjust the calendar. Although he was burned at the stake on February 17, 1600 we can ignore the day of the year and just shift our calendar’s zero year forward 1600 years. This has the advantage of being easily translatable to the Gregorian system.

If it really were to change, I’d actually go for the first space flight. It would highlight the advances in science we’ve made as a species, and not glorify any one person for the efforts of advancement which has been given by countless individuals.

But realistically, I don’t think it’s worth the effort. Every piece of writing referencing a date would become incorrect, and everyone would have to learn the conversion. Computers would need updating, etc. etc..
Now, making the change in computers would be simple, but it grows nightmarish when you consider how one human error in implementation could have far-reaching and negative consequences, such as for bank records.

So, I say we keep it as it is. But the foremost reason? 1 A.D. was not the year of Jesus’ birth. It serves to highlight how a people who relied on faith over science made a mistake, and remind us how we got where we are: science and reason.