There's an official way to do this on a Windows Phone 8.1 device with Cortana:
- Open up any camera application
- Look on the menu for 'Lenses'. Tap it.
- Browse the lenses on the phone for 'Bing Vision'. Tap this.
You're then back exactly where you would have been after tapping the little 'eye' icon in the Windows Phone 8.0 interface and can scan products, sites and apps to your heart's content.
It's not exactly elegant though. Thinking laterally, the easiest and most foolproof way into this functionality would be to ask Cortana to "Scan a QR code" - surely this can be added by the Microsoft teams? Or even, at a pinch, to ask Cortana to "Open Bing Vision", though that's not exactly intuitive. But both very easy, should Microsoft want to play ball here.
In addition to the guaranteed way in through camera lenses, above, there are also third party QR code readers, each of which can also follow up hyperlinks using Internet Explorer (and thence to the Store, if required):
- Red Laser, free
It may be free, but it doesn't work very well on most phones - an update definitely required from the developers - the last such was in June 2013!!
- QR Code Scanner, free
Thankfully, this seems to work much better, and was last updated in February, so hopefully there will be an 8.1-tuned version out in the next few months.
Recommendations welcome for other QR code scanners for Windows Phone - what works for you, other than Bing Vision? It's not definite that the latter will be around forever, but I don't think Microsoft will get rid of it for a while - or at least until Cortana has been taught what a QR code is!