If people want mkv support, more codecs, 4K now then you don't get the new Apple TV. It's as simple as that and no amount of second guessing will change that. Every media player has its pros and cons. Apple products are not for everyone. Heck a Kodi unofficial Android TV will give you every possible codec possible if that is what you are looking for. A Roku will give you certain things but not access to iTunes. If you want a multiple codec player then the ATV market not be for you. This constant request for the mkv container is so strange coming from people in an Apple forum. There's nothing wrong with MP4, etc... except perhaps it doesn't appear as the container of choice in HD torrent sites.
As I've said previously, the Roku is a fine player. It has a poor warranty, generally underpowered hardware ( at least the Rokus I had up to the Roku 3- can't say about the 4) and a bunch of channels that are hardly stellar. It does not have the developer support of Apple, Google or even Amazon. In my opinion, and this is just speculation, it has no future. It's a quick fix for now with a really weak evolutionary path.
As far as 4K it is still evolving. In particular streaming and wireless casting for it are not ready. Apple doesn't carry any and other streaming sites have next to no content for it, none with HDR as far as I know ( could be wrong here as that seems to be yet another issue with 4K).
I doubt Apple will ever support mkv, xvid, avi, divx or other containers. They have settled on a very good standard and really have no need to. It's not as though there is a shortage of players for iDevices that can handle these containers with no loss of quality. Good riddance to all these crazy containers and codecs. The world should be settling on fewer and whatever the standard ends up being it won't be mkv for many of the same reasons you will never see Kodi on an iDevice ( unless altered).
The new ATV doesn't even handle HEVC, which will become the new video standard.
And no, there's nothing wrong with MP4, but flexibility is a virtue in a device like this.
Someone mentioned Plex can handle all file types and containers, but Plex has to transcode the files to a type that's compatible on the device. If the device natively handles MKV, no transcode is needed.
As for Roku, specifically, they have Google Play and Amazon, so I don't know how you can say it doesn't have their support.
The ATV seems like a really nice piece of hardware. The Siri integration will be awesome. But some of the omissions from this gen seem puzzling, or at least they would seem puzzling if it weren't obvious that next year there'll be a new Apple TV that addresses the shortcomings of this one.