Does this means that it will likely be in a release prior to version 28? I'm not too familiar with Emacs release scheduling.

No, if it has been merged into the master branch, it will be released with 28.1.

Native compilation will need to be manually enabled on init.el or is already enabled by default?

Currently (with the native-comp branch) you have to enable it in your init.el, I assume that behavior will remain.

E.g.:

  (setq comp-speed 3)

Use comp-speed 2 for Emacs as a whole though. 3 will break some semantics of the language if I understand correctly.

Good to know, thanks! Hasn't bit me yet, but my config is fairly light.

From an Quick google I was unable to find any benchmarks. Does anyone have any anecdata?

I started using the native-comp branch a few months ago and have had no issues. As for performance, I haven’t benchmarked but things are noticeably faster and smoother. I’m on macOS and my main issue was the display going blank for a few milliseconds, and I’m no longer seeing that so a huge win in that regard! General search and completion seem faster too

There are some benchmarks here (elisp-benchmarks package): https://akrl.sdf.org/gccemacs.html

Feels like 10x faster