The legacy classification rule builder is being sunset Aug 31, 2026. So there is still plenty of time.
Ideally, the best thing to do is to start migrating your classifications over to classification sets. Rather than having separate places for the classification importer and the rule builder, they will both now be in the same place. Any classifications that you have that are using the importer you can migrate now. There are also some new options for automating the imports to make it easier to maintain.
However, if you're using the rule builder (for stuff such as regexing values), it doesn't seem that the rule builder portion has been released into the classification sets yet. I would suggest reaching out to customer care to see if they can provide any information on when it will be updated, especially if you're looking to start migrating your classifications.
So while we do want to migrate rule builder classifications, we can't do it quite yet, although hopefully Adobe will make that available soon!