All the cons you have mentioned have already been voiced over the years.
With Sky being bought by Comcast, I think Comcast will be making sure that the streaming service is up to scratch. After-all they are planning on launching a similar product to Now TV in the States.
1. Cheaper version of Sky
Sky own Now TV, and Now TV is seen as Sky lite without the contract and fewer channels and functions such as recording.
1. Quality is SO last century (720p for most its existence when others offered 4k). Even latest "1080p" is joke!
1080p is not the only downfall to Now TV, their 25fps make the Sports channels unwatchable at times. However 1080p is on its way, that I can guarantee! Although full launch, was meant to be last year and pushed back, my guess is either end of the year or start of 2020.
2. For £7.99 (£8.99 in the future) you get entertainment pass (tv shows only - movies/kids content for extra money)
Still far cheaper than Sky TV and apart from a couple of channels you get the main and important ones for over 50% cheaper
Movies and Kids is extra ££££ on Sky TV, so not sure what that final point was.
3. Audio - english only. Subtitles - english only and if you lucky.
Again also coming is 5.1 surround sound, which I can also guarantee, same timeline as 1080p
4. Its app very rare on most of the devices. Had to use laptop/tv connection through hdmi cable.
If you have a Samsung or LG TV, then it has the built in app. Or most people pick up a Roku Stick (not the Now TV stick) for £30 or more and you get Now TV along with most other apps.
That being said, Comcast have recent;y allowed their TV product on Amazon Fire devices. So I suspect sometime we can expect Now TV to be on Amazon Fire devices and vice versa with Amazon being on Now TV devices.
5. Limited time to watch shows (xx days to watch). And then they disappear.
This is nothing different to Sky, or even BBC/ITV/ALL4. The rights can only be purchased for a certain period of time.
6. Did i mention that their "update" to fullHD/1080p is ABSOLUTE JOKE?!