As of now, WhatsApp is quite restrictive when it comes to chat history syncing, only supporting a single phone number rather than an account. Well, according to a reputable source, Facebook is working on making your life easier when changing phones.
WhatsApp’s developers’ team will soon let you migrate chat history from one phone number to another, which is pretty useful for people owning two phones or who plan on changing their phone number. They also seem to be working on cross-platform sync because right now, you can’t transfer your chat history from an Android phone to an iOS one and vice versa.
The feature is not yet implemented and there’s no way of telling when it will happen. But given that even screenshots have already leaked, it probably won’t be long.