I've been using XBOX Media Center for years as well, but the cool thing about this is that you don't have to put up with the XBOX's limited resources, therefore you can watch movies in higher resolution than what the XBOX would allow.
If you wanted xbmc with full hd, then you dont need to spend any more than £200 for a completely system capable of 1080p h264 decoding in hardware, hence, I don't know of any reason to run aros in this case - for an htpc xbmc will do much better.
XBOX1 is still great for emulation as you say. Everything just works, with controller already nicely mapped for most stuff. as they can be picked up for next to nothing, and softmodded, they are still a viable solution so many years later. and of course xbmc (now xbmc4xbox) is still developed a bit.