There are nightly builds published here: https://confluence.jetbrains.com/display/SCA/Scala+Plugin+Nightly
The last version published there is at the moment: 2017.1.335
I have version 2017.1.327 installed (manually) and when I try to update it, I get "your IDE and plugins are up to date".
I do have Nightly update channel selected. It stopped working some time ago, only for the Scala plugin, probably a week or more ago. I hoped manually updating to a more recent version would fix it, but today I notice it didn't. Other plugins auto-update just fine.
Maybe the repository URI has changed? What is the current one? I have this one: https://plugins.jetbrains.com/plugins/nightly/1347