I would like to see a mild tweek in terms of the way spell costs are tabulated. The change I propose would be simple to incorporate and would increase the value of certain perks that are a tad weak as they stand now. More importantly it would make more viable the concept of building a true Archmage.

The nature of the change would be to make the perks affecting spell points costs( Novice-Master) in the various schools additive reductions rather than multiplicitive as they are now. Put another way, I am arguing that they should be made to stack with either; A) the skill point discount to spell cost or the gear deductions to sp cost, in an additive manner. The result of this would be, with a hefty investment of perks, a character that could claim to be a master of all schools of magic, an archmage.

The proposed change would look something like one of these two models, counting all non-exploit based utility:

A) Maxed skill discount 40%+50% Perk Discount*1200ish Magicka cost master spells = approx. 120 Magicka Master Casting

This of course could be reduced further with gear. Maximal reduction on an Archmage build would be approx. 40% in 4 schools, 65% in primary school. This would be approx 72 Magicka for 4 schools and 42 Magicka in the primary school.

This assumes 100 skill in all six magical skills +34 perks minimum(these being max enchanting middle path and all schools spell point reduction perks. It also assumes appropriate enchantments and gear.

Considering the power of magic relative to martial this is by no means unbalancing but in it's own right judged independently this would still be a reasonable change to allow a style of play not well supported.

Incidentally I fully realize it is possible to make either one or two schools of magic completely free to cast. That is fine and well. What is lacking is the Archmage option. This would resolve it nicely allwing many, many castings of weak spells and several but not infinite casting of any spell school for high grade spells. Such a change would still require said Archmage still have a relatively deep Magicka pool as appropriate for a mage. It would simply allow for a few more castings and make the magicka reduction feats more viable and worthwhile. As they stand now they are more a perk tax to reach deep set abilities that are desirable. There is another option that would have similar effect though with mildly different coding but a different flavor. Personally I find A preferable.

Maxed skill discount 40%*1200ish Magicka cost master spells = approx. 720 Magicka Master Casting

This method relies on perks being additive with gear instead of base skill. 50%Perks +15% +25% = 90 % reduction in appropriately enchanted geared and perked schools for 72 magicka/cast with one and only 1 school of magic capable of being made primary. Said primary school in this instance would be cast free of magicka. Note that in the vein of a non-Archmage(5 schools caster+enchanting) this method would allow 3 schools of magic be cast free rather than the current 2 that are possible. Method A would not allow this. I find that 2 schools for free should be ample to a "non-caster"(someone who need spend no resources toward magicka).

The current method, by contrast, is rather harsh for an Archmage(5 schools of magic+enchanting). It resolves this way: (.6 skill*1200 Magicka)=720 Magicka (720*.5 Perk)=360 Magicka for a single Master Casting with max skill and max perks. Remember that at a max(sans exploits) 4 schools of magic can be reduced by 40% with the last being reduced to at most 65%. That would mean your 4 schools have a Magicka cost of around 214 Magicka/cast while your primary school, IF you forgo..say Magicka regen or Magicka pool..or I dunno ANYTHING else then your 5th school would cost 126/cast. That is likely 2 maybe 3 casts before needing to slam potions for one SUBSTANTIALLY invested in Magic. Yes they are Master castings and thats what master casters should be able to expect to cast. Yes, it is also in all schools. If you level all schools you probably want to reasonalby be able to use all schools, don't you?

In short the Archmage, as stated, is not well represented and could easily be better represented with a simple bump in the calculation. Make the perk discount additive to skill please.

Yes, these numbers can be wiggled 3% sans exploit with another skill maxed. It isn't worth complicating the data with.

This would probably best be implemented in a mod (assuming you have the PC version of Skyrim), because Bethesda is not going to change how the magic system works (especially since they are done with Skyrim). If you are a modder or know someone who could make one, this would be your best shot at having something like this in your game. Interesting idea though.