Twitter characters can actually store up to nearly 31 bits each, if you’re using the JSON API. (Or at least, this was true in 2010. I don’t know whether this is still true.)
From the conversation in the hacker news link, it looks like base122 gets the increased efficiency from using unprintable control characters, which is incompatible with base65536's explicit goal of only using printable non-whitespace characters in its output.
https://blogs.oracle.com/ksplice/the-1st-international-longe...
Twitter characters can actually store up to nearly 31 bits each, if you’re using the JSON API. (Or at least, this was true in 2010. I don’t know whether this is still true.)
http://blog.kevinalbs.com/base122
https://news.ycombinator.com/item?id=13049329
Base-122 encoding is 87.5% efficient in UTF-8, better than anything listed in the base65536 repository’s comparison table.