Hi Søren,
disabling some (or all) products for a specific platform is included in the next major update, where these products are not handed over or fetched by Unity IAP to begin with.
It is ok to have all product identifiers in one build. Unity IAP will report back that it did not find some of the products, but that does not break any other functionality.
Do I need to add all the iOS IAP's (as dummies/standins) to Google Play ? or do I need to delete the iOS IAPS every time I build for Android ?
Depends on what you would like to do - you can have all identifiers in the IAP Settings editor as written above, but e.g. in separate groups. One for Android with all Android identifiers, one for iOS. If you let the ShopManager instantiate products in your shop automatically, you could destroy the container component for a platform in Awake.
So for example, when running on Android (#if UNITY_ANDROID) you could destroy the container component / game object for the iOS category in Awake. The ShopManager will not be able to instantiate shop items for that group later on.
As mentioned above, support without coding will be coming in the next update.
Currently Restore doesn't do anything on Android, but purchasing an IAP that have been made previously restores it.
Restore on Android is automatically invoked by Unity IAP, at the first app launch following an app uninstall and install. Triggering the restore process manually (I guess you are refering to the Restore button) does not have any effect indeed.