Sharing this article in an attempt to help folks join up the dots from the information currently available.
https://cloudblogs.microsoft.com/dynamics365/bdm/2019/05/22/the-future-of-dynamics-365-for-project-service-automation-psa/
It is obviously more focused on Dynamics/PSA and isn't necessarily specific about exactly what the future holds for Project Online, but there are some inferences that can begin to be drawn. Future licensing - always a worry - raises a question about customers using Essentials rather than Pro/Premium licenses which are mentioned as the only options.
I'd really welcome some sort of 'Project Online - Migration paths to new Project Service' article to introduce a little clarity and help organisations to prepare for the move. This sort of clarity is particularly pertinent for Project as by its very nature its current use commits organisations to systems/processes for the future that have lifespans that are closely coupled to the lifespan of the projects themselves.