Chromium will still contain this change, in fact its where it will appear first.

I wonder how they're going to make it hard to maintain the current webRequest API capabilities.

Can you elaborate on what this is and why you think it’s so great?

Ungoogled Chromium is Chromium with all google domains and google-specific code removed. It keeps the nice things about Chrome/Chromium like the dev tools and is compatible with Chrome extentions, though you do have to download and install them manually. Unlike Chrome, it is also 100% open source.

How timely are updates? Would be my main concern here.

I was under the impression that Chromium had some Google integrations but was pretty harmless from a privacy standpoint unless you sign in to Google. Is that wrong? Do I need to use Ungoogled Chromium instead?

It's a fork of Chromium, the core layer of Chrome, with Google integrations removed (and other privacy-conscious feature removals/additions).

https://github.com/Eloston/ungoogled-chromium

How is this different than Brave?

Brave is based on cryptocurrencies and selling eyeballs, with users getting a share. It's a for-profit startup.