Actually it goes all the way back to Arena. http://www.uesp.net/wiki/Arena:MagicIn Elder Scrolls: Oblivion, Spell Crafting was a feature where you could make your own custom spells by combining the effects of other spells, and altering certain attributes (I don't believe the system existed in Skyrim, it may have been in Morrowind though). For example, if I were making a summoning spell, I could take bound shield, bound armor, and bound sword and fuse them all into a single spell, then alter the duration (which, in turn, effects magicka cost). The end result is a spell that makes you completely ready to fight, even if you have no gear at all (very useful for parts of the game where you have to leave your gear behind.
Having a similar feature in ESO would offer a ton of customization options/variability for our builds, but it'll likely be difficult to implement/balance (imagine how potentially overpowered being able to create/customize your own skills is). There's no way it'll look like what the system did in Oblivion, I do believe that Zenimax talked about using some form of it at one point or another though.
It is the hopes and dreams of many in this game
It is the hopes and dreams of many in this game
Agreed. Unfortunately our hopes and dreams where shattered a few months back, when ZOS told us that they stopped working on it. Now we are not even sure if they have any plans of implementing it sometime in the future. The biggest problem people have with the discontinuing of development of spellcrafting is that ZOS already showed vidoes how it will work and a few example spells.
Now we just hope that the lesser used skills we have will finally be reworked/rebalanced so they are viable (without making already viable skills obsolete).