I got rid of K7 almost immediately. I did some quick testing, and had no issues.
I always worry about templates though. I have a (close to) 2500 track Cubase template, about 80% of which is Kontakt. Cubase/Kontakt support some feature in VST 3 that automatically replaces an old version with a new version. Again, it worked beautifully this time. I opened up my template, Cubase gave me a quick notification, and it was all automatically moved to K8. Very cool.