AppleTV does not officially support browser based content, but there are a few open source projects which get around this limitation. For example, Ejecta - Impact
It seems like it should work, and considering the most recent (Gen5) AppleTV is based on the Apple A10X Fusion CPU/GPU, which is the same processor used on the 2nd gen iPad Pro, performance should be quite good. However, I can find no reference to anyone building anything for AppleTV using babylon.js.
Ejecta sort of looks like the future BabylonJSNative or Exokit. They are programs that emulate a stripped down browser with just a webGL canvas. If AppleTV does not have a browser, then this will be your only route, other than maybe Exokit. Not sure if Exokit has an iOS port. Exokit is Node / WebXR oriented. An actual Objective-C app seems better for an Apple product. Thanks for bringing it up.
Ejecta says can make an openGL application from a WebGL workflow. They mention ThreeJS by name. Seems doable.