Update! I’ve pushed Whisperfish 0.6.0-alpha.4. I do not have the rights (yet?) to edit my topic start, to update the overview, or is that not-done here?
Either way: I am quite confident that at this point, Whisperfish is usable for a lot of users! 
Implemented features:
- Registration
- Sending attachments
Notably not implemented:
- GroupV2
- UUID-only devices
- Creating new conversations (contact selection)
- Group management (creating and modifying groups)
- Linking devices (i.e., Signal Desktop)
Known issues
- New 3.4 installs (the ones with
defaultuser) will panic on displaying messages. (fixed on master) - Entering a phone number for new messages doesn’t accept leading
+, but you can just leave it out! (fixed on master)