Brave isn't implementing v3 immediately, but Chromium is their upstream and I haven't seen them claim they will be able to resist indefinitely. They have their own non-extension adblocker for which v3/no-v3 is irrelevant.
The tweet you're referring to in the GP simply says "Brave will support Manifest V2 extensions such as uBlock Origin even after Chrome stops doing so". Which would be true statement even if that support only lasts for a day after Chrome stops supporting V2. That is to say, this does not look like a guarantee of indefinite support by any means, but rather extended support (for an undetermined amount of time).
Instead of getting attached to semantics, how about looking at it from the perspective of business and economics?
If your business depends on the idea that Big Tech can not track you, you need to do whatever it takes to keep it a reality. The cost of supporting a fork of Chromium might be too much when you are starting out, but when you are already a company of 100+ employees and 60M+ MAU, it becomes acceptable.
So, yes, if I had to guess with the information currently available, I'd say that Brave will keep away from v2 as long as it possible and as long ad the user base shows that this is what they want from their browser.
But Brave does, as mentioned before, have their own built-in adblocker (based in part on uBlock Origin), which doesn't depend on extension features. uBlock Origin does still have some additional functionality that the built-in "Shields" don't, but mostly it's not dissimilar. So, given that an ad-blocking experience on Brave doesn't depend on extensions entirely in the first place, I would think that would be a business/econ reason why they may not want to divert lots of resources into maintaining v2.
(Not sure where 'semantics' came from in the first place here.)
