We plan to support Screenly on the Raspberry Pi 4 in early 2020. Screenly will only recommend hardware that we know will deliver reliable performance for our customers, and the initial firmware released with the Pi4 is not sufficient to provide that. But, work is progressing quickly at Screenly and in the Raspberry Pi community at large to address these shortcomings, and we are excited about the possibilities that the Pi4 will offer. We currently expect to have a version of Screenly for the Pi4 in early 2020. Then, look for 4K video functionality to come in a software update in early 2020.
If you are interested in being a beta tester for the Screenly's paid edition on the Pi4, please submit a support ticket with the subject "Pi4 Beta" expressing your interest, and we will notify you about opportunities as they come up.
If you are looking for more information on running Screenly OSE on the Pi4, please check on the GitHub page https://github.com/Screenly/screenly-ose/issues for the latest information.