Slightly unrelated: I love that Carmack uses backslash (\) to escape 'EOL' and signify that this will be a thread and not a standalone tweet. Much more programmerly than "1/n" and "Thread".
On the other hand, null-terminated strings are avoided by most modern programming languages, which tend to explicitly store the string's length.
the 1/n scheme indicates the length of the sequence upfront, whereas the backslash scheme doesn't.
I've seen a variation of the 1/n scheme that literally uses "1/n", "2/n", etc. to avoid specifying the length up front. Usually the end of the sequence isn't indicated in that case.
There's something to be said for writing where your audience is. Carmack isn't a blogger and doesn't often write longer posts.
For me, I have no problem reading threads on Twitter. I look forward to the daily one from Foone. But if you put someone who hasn't used Twitter much before in front of this interface it becomes apparent very quickly how poor the UX is for threads.
Right now, we're discussing the various symbols people put in their posts (which are severely space-limited!) to indicate that there is a thread. Why is this necessary?
For sharing purposes, you might try using one of the "thread unroll" services to get around this issue.
There should be a word for people like that...
It's neat how fast a good convention spreads.