Since MediaWiki 1.5 (2004) a feature $wgLegacySchemaConversion is added. I don't think how it is useful now, given we already migrated another place to store content (T183489: MCR schema migration stage 1: Fix Legacy Archive Rows) and the text table itself is going to be emptied soon in Wikimedia wikis (T183490: MCR schema migration stage 4: Migrate External Store URLs (wmf production)).
It seems Wikimedia is still using it (cur.ibd in T54921: Database tables to be dropped on Wikimedia wikis and other WMF databases (tracking)), they should be migrated.