I would like to create a media center application using ElectronJS to facilitate video streaming/playback on the raspberry pi. My question is, what's the best resolution I can hope for smooth playback with across each of the raspberry pi devices if they're running linux?
Electron alone might manage 720p@30fps , but not full HD on the Pi. Launch and control omxplayerGUI from inside Electron instead , it should manage full HD.
Read the manual , especially section 9 ("Developers Section").