Given that the magic system has changed there would have to be a new way that spellcrafting worked.
Perks:
Before spells fell under one school, no matter how many there were. However now that wouldn't be an option as the perks have more influence over spells than plain old skills did. Whether it be reduced mana, distance, or length, perks allow us to influence spells in a more detailed way.
To solve this the game would have to split the schools into multiple schools. When you create a spell each spell would be influenced by the given skill tree. So if you have reduced mana for novice spells in both alteration and destruction the spellcrafting would take that into account. The only question would be about perks that influence things like duration, or distance which were variables you could previously manipulate.
Skill Tree:
There would need to be a skill tree for spellcrafting like there is for enchanting, alchemy, and smithing. A similar style would be appropriate where you level up your spellcrafting and it gives you access to more control. I don't believe any perks reducing the mana cost of spells would be balanced as it would become almost like double dipping, however I have some ideas.
Perk (style) 1: Allows for the player to have access to novice, apprentice, adept, expert, and master spells.
Perk (style) 2: Allows the player to have more control over the variables (such as damage)
Perk (style) 3: Allows for for base mana cost of spells. Meaning that before this perk spellscrafted would have a higher mana/spell point ratio than the base spells.
For example the standard ratio for the base flames spell is 14 mana per second to 8 damage per second. The ratio of this would be 1.75 at a base level. However under spellcrafting it would be 3.5 (two times as much, maybe 3 depending on if there are multiple perk 3's).
One could argue that this is stupid as spellcrafting should be related to magic, however it fits the current system, and the way people view skills.
Casting Types:
One of the problems I see is how spells are cast. Before there were really just three ways to cast a spell. You had touch, target, and self. When you summoned a familiar the familiar would basically appear beside you. In Skyrim you have effects like Flame which are constant, you also have runes, conjuring spells that allow you to say where you want to summon, magelight that sticks, and self spells.
Problems come in when you want to combine a flame spells, with a conjuring spell, and maybe a rune. Since there is no the ability to hold your spells and aim you're kind of stuck between 3 animations, and 3 different ways to cast the spell.
A work around would be to have a system like you have before where you pick what it'll be (touch, target, self) which could lead to some cool effects like magelight that sticks to an enemy and explodes, or runes that heal when stepped on (you could place them behind you and retreat if needed). However the problem of animation still comes in, and how the different types would ultimately work.
Without spellcrafting you're not stuck to 3 types of casting that work together. You can have these different types of spells because you don't have to worry about how they'll work when combined.
Perk problems:
Another problem is the effect perks have that extend the duration of the spell, and the distance. Would you allow those to affect spellcrafting? Do you allow for the player to create a rune spell that has a distance of 1 but then becomes multiplied by 5? How do you determine the difference between Novice and Master spells? How do you determine staggering?
Complexity:
As you can see with the introduction of perks the system becomes a bit more complex. You have a lot more influences affecting the spell, and ultimately its outcome. I'm not saying it requires a spreadsheet (although one would definitely help) but you'll need to do research and the different multipliers, and behind the scenes math will need to be given to the player in some form.
Other ideas:
If spellcrafting were ever implemented in some way I'd like to see them take it a step further in two ways.
1: I'd like to see it become more... natural. Have there be negative effects to spells you make (like alchemy). Have spell making be similar to Magicka (the game) where the spell you create could work against you in some way and kill you, or harm you in some way.
2: Add sequencing. I want to be able to throw a ball of magelight and have it blow up after a certain amount of time. This would allow for much more control, and better outcomes. I'd like to have a rune that paralyzes the enemy for 3 seconds, then as they rise it would explode, or calm them.
#2 is definitely broken as you could set up a chain of paralyzing. You could set up the first paralyze for 2 seconds, then have the second paralyze act after 2 seconds, and so on.
I don't intend for this thread to be used to discuss why spellcrafting should, or shouldn't be in the game. That gets us no where as it is nothing more than our opinions. I'd like to hear ideas for how this could, or would work. Proposing ideas will at least help to understand why it wasn't, or why it should be in the game. It may even help for mods to implement the idea... I'm probably being overly optimistic though.
