There's no need to bash others for something they'd like to be added into the game. I quite liked spell creation, and it would have been a good addition to Skyrim as well.
While I do agree(and disagree highly with Shroob's condescension), he unfortunately has a point. A lot of spells have their own unique behavior now(lightning's instantaneous speed, fire's ability to ignite the ground, ward spells breaking under magic etc.), so making a spellmaking system would be difficult at best, straight-up impossible at worst