My expectation is that it will come in a future release but I would not expect a timeline. Even when you have a NDA with VMware it's very difficult to get them to disclose new features.
With Horizon 7.7 they added the following so I expect it's forthcoming.
Release Notes for VMware Horizon 7 version 7.7
Horizon Agent
- Windows Server 2019 is supported for RDS hosts and virtual desktops.