One small difference... you can buy cables with any kind of end on them... Type C to Type A... for instance. At least it's possible to utilize the new Type C port with your existing devices. On the other hand... you can't do too much with a 4K streaming box unless there's a lot of 4K content.
A 4K

TV would still play 1080p at its MAX. Any 720p content would also play at it's MAX. It's not like adding an emerging technology means that ONLY the content for that emerging technology could feed the box. A 4K

TV linked to a 1080p TV simply means great 1080p displayed on that TV.
The reason to make "a lot of 4K content" available will be driven by profit. Could any studio put a lot of 4K content in the iTunes store right now? Sure they could. So why don't they? Where's the

TV that can play that content?
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If Apple had put 4k on the doorstop everyone would have been jumping for joy, but because they haven't we all of a sudden don't need it.
That's how it is. When Apple still clung to 720p, these exact same arguments were being made against 1080p. Then, when Apple embraced 1080p, all those arguments so passionately argued against it evaporated. See opinions of bigger-screen phone screens when Apple deemed 3.5" and then 4" as "perfect" or how gimmicky NFC was before Apple adopted it.
This is exactly the same. Right now, we believe Apple is going to be against 4K in the next

TV, so 4K is stupid, useless, human eyes can't see, file sizes, "the math says", and so on. Then, if Apple does surprise us and roll out a 4K

TV, it will be gushing love and "shut up and take my money".
Personally, I don't have a 4K set today but I'd MUCH prefer the next

TV come with the capability even if I couldn't exploit it until I step up from a 1080p TV set. The rumors are that the next one will have an app store and some kind of cableTV subscription "new model". If true, Apple will probably sell tons of these boxes. If so, all that volume installation of 4K-capable

TVs will be enormously tempting to the Studios to offer 4K content in the store. In short, if we're thinking we get to 4K for the masses in a few more years, Apple could lead the way there.
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What makes me NOT want 4k is the streaming. Sure, I have a decent internet connection, with 22 meg down, but I still see plenty of stutters in streaming video. Google tells me it is because AT&T isn't a quality ISP for HD content.
4K content would not be forced on anyone as the ONLY way... just as those who don't want the 1080p version of something in the store now can opt for the 720p or SD version. If there was a 4K

TV, some content would probably offer a 4K version of the file... ALONG WITH a 1080p, 720p and SD version.
In your case, you just go with the right version for the hardware you have. In other's cases, they go with the right version for the hardware they have. While you have just purchased a 1080p TV, lots of other people just purchased 4K TVs. Apple could feed their sets maximum resolution streams while still feeding your sets your own maximum resolution streams. Everybody can win.