I have some assets that broke with 2018 because of substance being removed and now exist as a plugin. Some of these artists will remove the substance materials and replace with static ones because they can’t afford the bad reviews the error might result in.
This is very unfortunate for us game Devs as it means less customization. What unity needs is a nuget solution were the asset store artist can declare dependency upon another asset. This asset should be downloaded and installed before the dependant asset.
In the store you can present these dependencies, and if the dependency is a paid asset the total price of all needed dependcies including the asset itself could be displayed along side the assets price.