I just don't see spells bringing true value to the game especially the end which was stated in the video. Personally, I feel that the cost in terms of relics is a little over reach for the amount of time and resources it takes to either negotiate with goods or cost with your army in terms of supplies and to lose in the end to spend more in valued relics for a short boosted time to pump up your workshops for additional supplies which in the end still will not cover the amount lost over 8 battles for the province. I think its a good ideal but it doesn't offer value or added benefit to the player to compose the building. Also for the other boost like added time for help on a cultural building kinda duplicates what the AW does at a fraction of the cost and its permanent too.
I'm ranked 3rd in my realm (Over 100k Score) and I have all the AW's. I do have space to add the new building but honestly I would because its new but I wouldn't use it. I feel the direction of the game going to spells is fun and all but it doesn't align to my needs as a player or others too. Even new players couldn't get real use out of it for the cost being relics for reasons stated above. If you want to keep spells then I suggest to have them cost in goods, supplies, coins or even just diamonds. Relics are for boosting your goods production and Ancient Wonders and no offense this Spell Building is no wonder.
To keep me more involved in the game I like to see ALL buildings have value in terms of score, AW's & Dwarven Porthole don't provide additional points which they are the most time consuming buildings to build and expensive in terms of Goods, Relics, KP and Time. Also I like to have more space or expansions if no new race/age is coming out soon.
I don't want to take away the fun factor from the game but with spells it doesn't add it too. I like Elvenar just would like to see the game focus on the players suggestions while adding quality content.