The fork exists as a ‘buffer’ to get some changes (features or bug fixes) out without the need to couple with the npm release of rrweb itself. Sentry engineers have several PRs in upstream rrweb merged and the goal is to increase the upstream contributions and close the gap between our fork and upstream. We’re currently porting our changes from v1 to the v2 branch.
I believe Sentry has made financial contributions to rrweb but directly to a maintainer. I'll let others who know details to comment on this. I'm sure more contributions will be done, as this is very much in the interest of Sentry anyway.
Worth noting, Sentry has been making larger contributions to OSS every year, as the company grows:
2021: https://blog.sentry.io/we-just-gave-154-999-dollars-and-89-c... 2022: https://blog.sentry.io/we-just-gave-260-028-dollars-to-open-...
In addition to that, there are contributions to open source done in the form of code that is, open source, such as the symbolication service: https://github.com/getsentry/symbolicator and many others: https://github.com/getsentry/