I've found a device that is running both Windows 10 and Android 5.1. The idea of two systems is very appealing to me. Windows 10 would be great to play some games and using office and Android for everything else. The problem is that there is no use for basic Android OS without Leanback Launcher and Android TV apps. So is there a way to sideload Leanback Launcher and TV apps to basic Android? Has anyone tried it?
Nope. Android TV is more than just the interface to actually work right. You'll be missing quite a few perks of the AndroidTV OS.
There is the opengappstv thing, but by the readmes it's mainly cosmetic and for the rare ROMs on the cheap boxes. If you got recovery I can't see why you couldn't try flashing it. opengapps.Org hit the tvstock radial for your build. Make backups, good chance this will break stuff. There's also an app called HAL, emulates the leanback layout.
I'd personally get a dedicated w10 machine and a Android TV box myself. I have a feeling this combo device will be underwhelming if you don't have it yet.
Go for a $US69 Mibox and get the original AndroidTV experience, Nougat is an expected upgrade in the near future.
There are several platforms (Rpi3 and X86) where attempts have been made to port official AndroidTV. There are even generic tv boxes that have had Leanback Launcher shoehorned onto them.
While the pretty face of Leanback Launcher greets you on boot, the underlying technology does not allow for things we take for granted on real official AndroidTV devices.
Trivial aspects like a complete battery of support for various DRM licenses which allow for Netflix and other platforms to show HD or better streams and a little thing called ChromeCast. Support for HDR color intensification is another major fail for non AndroidTV devices.
I have a Nexus Media Player that has Chromecast and Android. But once in a while I connect my Note 3 via HDMI cable to watch movies too. Look at AVStream and Configurator apps both paid apps to give your phone that android TV like experience. Both use KODI. I was lucky to install AVStream on my Nexus too.
I would be happy just to be able to install the android tv version of the Netflix app on my tv box that runs regular android. Anyone knows if that's possible?
Possible, yes, but it can take considerable work and won't be the full Android TV feature set. Things like Chromecast and HD DRM support might not be supported, depending on the hardware. That being said, you can get a TV friendly launcher and sideload many Android TV APKs.