We ship the following package: https://github.com/zsh-users/zsh-syntax-highlighting R3330 but there exists a popular, faster & better-optimized fork that also has increased granularity with the syntax that it actually highlights.
I'd like to suggest replacing R3330's upstream with https://github.com/zdharma/fast-syntax-highlighting. It's pretty much the same, but better in every way. It keeps up-to-date, too. Last commit at the time of making this request was 8 hours ago.

I'll provide the standard package request information for fast-syntax-highlighting, to assist with making changes 'n' such.

• Name of the software - fast-syntax-highlighting
• Project Homepage - https://github.com/zdharma/fast-syntax-highlighting
• Why we should include this into the repository? - Faster, better optimized and increased granularity with highlighting syntax.
• Is it open source? - Yes. Uses exactly the same license as the current upstream. (BSD-3)
• How many users do you anticipate will use this software? - However many use Zsh with syntax-highlighting. (Probably quite a few)
• Link to source tarball/zip file* - https://github.com/zdharma/fast-syntax-highlighting/archive/v1.15.tar.gz

*The upstream developer seems to be quite cooperative and is happy to have this packaged by adding newer GitHub releases.
https://github.com/zdharma/fast-syntax-highlighting/issues/19

Since it's just a Zsh plugin, it'd be possible to have both packaged and they shouldn't conflict in any way that'd break things, but I think it'd be better to prevent unnecessary package duplication.

Comparison video available:
https://asciinema.org/a/112367

zsh-syntax-highlighting's old package request: T3342

TL;DR because similar naming: zsh-syntax-highlighting upsteam > fast-syntax-highlighting upstream, because improved & up-to-date fork.