Whatsapp may be working on a feature that lets you migrate your chat history from Android to iOS, according to wabetainfo via (Android Central).
The feature was first spotted in the latest WhatsApp beta version 22.2.74 for iOS. Appears to corroborate wabetainfo’s previous discovery in beta version 2.21.20.11 for Android.
Whatsapp will ask for permission before starting the transfer process. The app will then instruct you to keep the app open and your phone unlocked.