I’m not sure of a specific timeline, I’m sure it will be a couple years to make such a significant change to the network. As I understand it essentially all Zcash would have to migrate, not an easy task.
In the meantime here is Halo news you may have missed: Episode 123: Halo with Sean Bowe and Daira Hopwood from ECC - ZK Podcast
We’ll have a little bit of an update on the livestream next week.
Also there will be two ZK Study Clubs on Halo, one by Sean on the 18th of June, and one by me on the 25th of June, both at 17:00 UTC. Join the ZK Study Club Telegram group for more details 
The YouTube videos (which also link to the GitHub repos and relevant papers) are here: