True, though Apple Music and the iTMS aren't available on any set top boxes, video game consoles, smart TVs, BR players, etc.,. Going totally platform agnostic would be a major blow to

TV, but making

TV a mandatory purchase is going to hurt adoption since all the competition is platform agnostic. Apple's in a pickle on this one.
Though not currently on set top boxes, video game consoles, smart TVs, BR players, etc., for now Apple Music is almost entirely audio-only - a streaming music service trying to make headway on video platforms doesn't stand much of a chance. How does Spotify do in this arena?
However, the subtext for this article is Apple's continuing expansion into video programming. Apple
Music would be pretty poor branding for a video service. We can speculate as to whether it'll be a single service/subscription with a new name, or two separate services/subscriptions, but whatever's going to emerge is likely to be much bigger, revenue-wise, than Apple Music alone, consistent with the history of video entertainment vs. audio.
As to whether Apple would sacrifice revenue from

TV hardware sales... I think it's a no-brainer. A $129 set top box that might be replaced once every 3-5 years (if that) vs. a $10-$25 per month subscription that pulls the same revenue in a year or less.
Sure, the same could have been said about iPod, but I'd argue that the MP3 player industry was still in its infancy, while competition from well established set top boxes, smart TVs, etc. is much stiffer. Apple isn't in a position to create a new market segment this time, so there's less leverage.

TV will likely continue, and sales will likely grow, for the same reasons that Apple sells four times as many Macs today as when iPhone was introduced - the power of the ecosystem and the public's wider exposure to the Apple brand. Further, if certain content categories, such as games, remains platform-dependent (iOS/tvOS), then the proposition is, "You can view Apple Video content everywhere, but if you want the extra value/capabilities that come with

TV apps, just make a small additional investment in an

TV."