By the looks of it we won't be getting a beta of DSM 7 this year.
According to this ComputerBase.de article, looks like Synology will take some more time before pushing out beta version of their NAS OS, DSM 7.
The upcoming version will bring a lot of new features, under the hood modifications, C2 hybrid storage, and an online remote managment and monitoring called Active Insight.
These are just a few options worth mentioning but a lot more is coming, more on those features when I get hands on.
According to the news on the web, looks like we will get version 6.2.3 before or at the same time as beta 1 of the new version. At the moment there is no exact date but Q1 2020 is the time frame for the time being.
For now, we have to be patient and hope they do a great job.