The blur background feature is not supported in Skype for Business 2019 On-Premise. This feature is available in Microsoft Teams, but Skype for Business on-premise clients do not have this functionality.
Regarding future releases or updates, there has been no official announcement from Microsoft confirming if this feature will be included in any upcoming versions of Skype for Business, including the potential Subscriber Edition you mentioned. Microsoft has been focusing their efforts on enhancing Microsoft Teams, which includes such modern features. In this case, we recommend you give your feedback in this UserVoice page:https://feedbackportal.microsoft.com/feedback
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