Hopefully, it will not be good enough to fool us, even in a PDI, let alone a print. I would strongly advise against the use of this feature wholesale; with the higher resolutions available today and the more sophisticated expectations of judges from manipulated work I have grave doubts that it can achieve a high enough standard.
Why do you need it anyway in a real landscape picture? If you are picturing reality a new sky will invariably give an unnatural look and I remain to be convinced that you will not be able to “see the join” in any complex skyline.
This feature may have some use in montage work and more detailed work but I doubt its use in the manner demonstrated would ever be of use to us in real landscape work.
I posted an event on the events forum for Saturday, Rugby with forecast of Mist. You can view the results on the CPS Flickr site. This was a challenge to say the least, if you note the settings I was using you will see the ISO was about 600, the camera would not focus as there was no contrast. was hoping for a Moody shot with perhaps some steam rising from the Pack as they were in a scrum, could not see the scrum let alone the steam, Came home when the fog thickened before half time.