I would like to be able to re-register a new number without having to de-activate the account thereby not losing all of my chats.
Telegram allows using a username to mask sharing the phone number with new contacts, but its initial setup is based on the phone number and it insists on notifying everyone who has your number that you've joined the platform. Messaging platforms would be much better if they considered such things as privacy issues and provided more control in the user's hands, with sensible defaults and good initial setup instructions.
Another feature that I would like to see (Chat backup and restore). If it's there, I can't find it.
I can back up that Chrome point, unless it has been added in a recent update. On Android, it can do encrypted and plaintext backups - never tested, but I assume they include messages. What else.