Maybe? That gets sort of awkward for frequently updated things like Reddit where there might be 10 dictionary versions between what you have and the current version. You’d need something that decides whether to get an incremental update or a new dictionary, and the hoster has to store those old dictionaries. Feels like more trouble than it’s worth.

You could compress things with gzip if the dictionary doesn’t work well, but to my understanding gzip compresses repetition. There’s less repetition in smaller chunks, so worse compression ratios. Eg compressing each comment individually has a worse net ratio than compressing all the comments at once.

It would also be annoying to merge a bunch of individually compressed blocks back together, but certainly an option