The release date for the next update depends on what the dev has planned. If he uses assets that are featured in previous updates, the update will happen sooner. If he has to create completely new environments, like in EP8, the update will stall. Keep in mind the size of the bonus episodes he works on affect the release schedule, too. From the teasers so far it looks a big portion of the update will take place in the halfway house, which in theory will speed up the release. He started working on it a month ago, so my guess is a late July or August release, but we'll see.
EP1-EP2 - 19/07/19 - (00 days)
EP3 - 27/08/19 - (29 days)
EP4 - 13/10/19 - (47 days)
EP5 - 16/01/20 - (93 days)
EP6 - 17/05/20 - (122 days)
EP7 - 26/09/20 - (132 days)
EP8 - 25/02/21 - (152 days)
All EP9 Teasers so far: