Yes, Divinity 3 is currently under development. The official name is not known publicly yet; Larian is just calling it Project E.
Dragon Commander is expected to be released towards the end of this year. Project E should be officially announced by then, but we don't know when that will be or how long after Dragon Commander it will be out.
There are some links to what we do know quoted below from an older topic. Search for posts by Lar_q with 'status' in the title for later updates, or check out
Lar's blog, though there wouldn't be anything significant in them about Divinity 3.
There are lots of details out now for Dragon Commander, but not much about Project E (other than it having a top down camera view). See Lar's post
here for the first details of both projects, and there were some earlier comments in the older topic
Status update. The latest news on project E is in the more recent
Status update and
Status update (long overdue) topics. The most recent status updates of
June 9th,
June 23rd and
July 11th don't contain much info on the games (more behind the scenes stuff and other projects).
