ERB generation should be a lot faster, which will be a boon for a lot of Rails apps, and according to the release notes there's a 5-10% performance improvement overall from removing all trace instructions from bytecode.
Rails has not used the stdlib ERB implementation for a long time. As of 5.1 it uses erubi [0] and prior to that it used erubis. [1] So the performance improvements to the stdlib ERB implementation will not affect rails apps.
[0] https://github.com/rails/rails/pull/27757 [1] https://github.com/rails/rails/pull/16773