I created an implementation for this project It is available on Github.
Some documentation about the reverse-engineered protocol can be found on https://github.com/jpjodoin/sunshower/blob/master/doc/protocol.md
This is still a work-in-progress, but basic functionnality works. The current implementation has a basic REST API that allows to fetch the state of the system and toggle valve for X minutes which facilitate integration with home automation system like NODE-RED. There is also a very basic WebUI. More information can be found on the Github page.
Note: there is another implementation that was created by Kai. It can be found at https://github.com/FreshXOpenSource/melnor_decloudify