they'll move to threads because threads will be incompatible with the rest of fediverse (thread essentially defederate themself), and if most content is being posted in threads, they'll move there (since they can't access it from other instance)

this has happened before, such as

• MSN messenger breaking compatibility with AOL IM (MSN wins since it got 95% market share)
• MS Office doing obfuscation to their office file data to prevent FOSS editor like LibreOffice from rendering it correctly