I already have Chromecasts and I'm a big fan of them except for the fact that they're Wifi only :( Never really had a problem with this but I'd prefer permanent devices such as this to communicate via copper and leave my Wifi network dedicated to the mobile stuff. Disappointed that the Nexus Player also didn't have an ethernet port I started doing some research and found a few others have had absolute success using generic MicroUSB OTG LAN Adaptors and thought I might give that a go myself so I went on the hunt for a player. Tried Amazon US about a month ago but of course they didn't want to ship to Oz so then saw them on eBay from local sellers for around $190 but just couldn't bring myself to pay that much for something I'm only going to use a fraction of just as a basic Media Player running Plex. For some reason something made me try Amazon again a week or so ago and this time it worked!! AU$140.94 & 10 days later I have a Nexus Player in front of me!
Not the be-all-end-all solution for many but a hard-wired Chromecast is all I was really after. Embedded Bluetooth and other features are kinda cool though allowing keyboards & gaming controllers to connect to it so I might find myself using it for other things later on. Of course there may be regional limitations but I'm willing to risk that.
Here's a link to the OTG adaptor I bought for it however it hasn't yet arrived so I can't report on its success: http://www.ebay.com.au/itm/251774239717?_trksid=p2057872.m27… Note that it also offers USB ports so I can't see any reason why USB memory couldn't also be used. Again, it's a good 2-3 weeks away from arriving at this stage so I can't comment on this further.
Here's a link to one of the many articles on the use of an OTG LAN cable: http://liliputing.com/2014/11/surprise-google-nexus-player-s… and another about USB storage: http://www.androidcentral.com/about-nexus-player-and-usb-sup…
Hope this helps someone in the same boat anyway.
Be cheaper for you to get an AC router than this, Wireless works pretty good.