Apps can be version dependent so it's never a sure thing when changing iOS. And to rely on icloud alone for your files/data is crazy. It may be good but where is YOUR BACKUP?
As to what will happen, my bet is data will restore but apps won't for very good reasons.
I have an Iphone 5s with the latest IOS 8.3
Yesterday I got a new Iphone 6. Before doing anything I backup the 5s to iCloud.
I started my new phone and select restore from iCloud. Impossible to do it because the new phone was shipped to the shop with IOS 8.1 or something and all my backups are done after 8.1
There is a warning that the backup cannot be done because the IOS are not the same.
No written anywhere that restore from iClould only works
if new iPhone have the same IOS of the backups
What I did I just downloaded the IOS 8.3 to the new phone and because was of 552mb took long time.
Now I have a new phone with IOS 8.3 and all backups with IOS 8.3
I was thinking of: getting into reset Iphone setting and select: erase all content and setting, then do the set up again and select restore from iCloud.
Will it work?
If I do this will reset the IOS to 8.1 or to the latest 8.3 downloaded by me??
I really try to avoid downloading all my application one by one
If there is any other way to do it please let me know