I think it will be a while yet. If you go to the v4 api endpoint, you get this message

Making assumptions that v4 is still being actively developed, i'd say we still have another few major release cycles until its fully implemented/functional. Then I would assume that there will be another period of multiple major release cycles where both v3 and v4 are supported.

In saying that, i'm happy to be proven wrong, but in other words, i'm not concerned yet about updating various calls to the api

Yep @hkingsbury​ 

That's correct, we have no plans of deprecating V3 and when we do it, we will give lots of notice.

However, we are looking more seriously at deprecating our support of the JavaScript REST API, so if you are actively using it please leave a comment here.