I like the idea of the Holocene Calendar, but there were already archaeological sites known to be older than twelve thousand years when it was devised. As archaeologists find older developed structures and dating methods get more precise, negative HC dates get pretty likely.
Unless we didn't take the big bang as the first year, negative dates will exist. From an archaeological stance, 12.000 or maybe 15.000 years would be better, but 10.000 has an advantage: for anni domini we stay in the same millennium, i.e. 2016 becomes 12016, which is easier to parse at a glance than 14016.
I really wonder which +12.000 yrs old sites you're referring to (no rhetoric intended, I'm really curious).
That's equally viable, just like any multiple of ten, but I think that ten thousand is easier to parse, and that we won't find enough BHE events to use twenty thousand. Though my guesses and thoughts are uninformed here, and I'm mostly interested in middle-eastern and european antichity, not archaeology and geology.
