As you alluded to, many Chromium forks (notable exception is Ungoogled) are backed by tech companies. There's already plenty of intentional changes they maintain in their forks, like Privacy Sandbox,[0] so I don't think preserving support for v2 is a large hurdle for them.
[0]: https://support.brave.app/hc/en-us/articles/10742158329613-W...