We plan TeamCity 9.1 release for July, so this is one of the last EAP builds which is approaching release quality. We run nightlies on our internal TeamCity instance for a long time already and have just upgraded public test instance https://teamcity.jetbrains.com/ with the build.
The build introduces experimental ability for one way agent-to-server communication and bundles VSTest support which was previously available as a separate plugin. For details check the release notes or full list of fixed issues.
Apart from that we are mostly focused on polishing of the earlier introduced functionality and fixing bugs.
It's high time to try the build on your test servers and drop us a line if you find any issues with it.
BTW, if you missed the results of the TeamCity plugins contest, make sure to check the winners and all the participants on the plugins page.