AFAIK there should be no difference in server load, only client load.
Creating and destroying any effect that needs to be rendered cause load on both by default. You can optimize it now with Local Player value at certain conditions to take some considerations on when and how often to create effects and portion the load more on the client side, but still the server is invoked since it needs to register and check if there are any additional entities in the game instance.
I mean that it shouldn’t cause any extra server load compared to the standard effects.
It should not i agree, Blizzard might have another intention of adding such mechanic, or the effects affect other parts not specific on the load they may produce. What could be the difference between the standard effects and new effects would be a helper question which Blizzard may need to answer to gain a better understand why they cover the new possibilities in a currency system like this, all valid questions indeed.
Yes exactly and that is why there is an extension points system. You can only load so much effects in ram.
There should be no extra memory usage from additional effect types on the server. The server doesn’t have to render effects, it only has to tell clients which one to render.
Yes, but adding new effects means the clients could theoretically have all of them at once loaded, which is not possible when taking into account other stuff like assets or skins. This is why you get extension points by removing slots (therefore disabling the number of unique skins you can get) or putting workshop maps (therefore removing map assets). It has nothing to do with server load and everything to do with client memory budgets.