According to Roku's OS 9 release notes, the service will soon be available to the select devices that are getting the updated platform. The update will even give you the power to control Spotify via the Roku remote or via Spotify Connect on a laptop, tablet or phone. While OS 9 won't be be available for Roku TV models until 2019, you'll still be able to install Spotify on a Roku TV running OS 8.2 by adding it from the company's channel store.
Aside from bringing back Spotify to the platform, OS 9 also introduces Automatic Volume Leveling, which ensures a uniform audio level across programs and all types of content. No more startlingly loud sounds when a commercial comes on or when you switch streaming channels. In the US, select Roku players will also let you control iHeartRadio, Pandora and TuneIn using voice commands. The company has listed all the devices getting the major update on its website, so check it out if you have an older model and aren't sure if you're going to be part of the rollout.