According to The Verge, opting in for the beta build should keep chat history and media securely backed up, with the significant caveat that if a user forgets their passcode or loses the 64-digit recovery key, then they’ll be locked away permanently because even WhatsApp can’t get in then.
Those who are Ok with being on their own in that aspect, can get in the beta test group or wait for this to be available to everyone.
WhatsApp messages are encrypted end-to-end, which means prying eyes can’t easily see what’s there. However, on the current version, if a user keeps a backup stored in the cloud, authorities can use a search warrant to have Google Drive or iCloud hand over access to that data.
As per The Verge, WhatsApp is also testing a version that works across multiple devices, maintaining end-to-end encryption whether or not you have a phone involved.