Hi @Anonymous User
I doubt Amazon will be coming anytime soon on the NowTV Platform, where i would say Amazon are a more closer rival competitor against Sky than Netflix, where both Amazon and Sky Store offer movies to buy and rent where Netflix doesn't.
Like you i was glad to see the Netflix App added to the newer nowtv boxes and nowtv stick, where the Netflix App seems to be working great on my nowtv smart box
The nowtv devices are a stripped down version of the Roku players with a limited number of Apps compared to the full blown branded Roku player.
Unfortunately you won't be able to download any Apps from the Roku channel store on their website and transfer them on to the nowtv devices.
If you are looking for the NowTV App, Netflix App, Amazon Video App, plus BBC iPlayer etc all on one streaming device, then perhaps consider the Roku Express where currently they are being sold by authorised retailers for £19.99 as a Black Friday promotional deal (normal SRP is £29.99).