OK Mephe, let me go point by point through your suggested changes and discuss (this should maybe go in another topic, but meh... we're on the subject already)
1. Enchanting mana cost fix - I like your suggested changes. I may not be able to go through every piece of random loot at this time, but I'm hoping I can change the max values in the ENCH file, or the MGEF that is tied to it. (Will look into it). Not sure about blocking the fortify restoration potion exploit - honestly, people who go out of their way for this sort of thing are unlikely to download a "balanced" mod in the first place. It's a good idea, but just maybe not worth the extra effort.
2. Combat mana regen fix - By default, combat regen is 33% of regular regen. I upped it to 45%, 60%, or 75% depending on how hard you want to make magicka management for yourself (different players have different ideas of "balanced") 100% is a bit *too* easy from the feedback I received on my mod. I have no qualms with people stacking regen enchants if that's how they want to use them.
3. Casting mana regen shut off - why DOESN'T magicka regen while casting? I hate trying to aim a firebolt, waiting for the enemy to run back towards me, knowing I'm not regenerating mana all the while... what stinks is there's a game setting for allowing or disallowing NPCs to regen magicka while casting. Where's that setting for player characters?!? I'm hoping the CK will reveal more...
4. New spells that allow the mage to become safe for a short time and regen mana will be needed - Will they? What's wrong with the Become Ethereal shout?
5. Spell cost versus damage issue - I handled this a simpler way. There's a multiplier based on proficiency (skill level) that affects how much spells from that school cost. I increased it on all three versions of my balance_magic .esp files. (increases the discount so all spells cost less as you get more proficient) Obviously, the easy version got the biggest proficiency based discount, while hard was only slightly more discounted than vanilla.
6. Add 6 more perk levels to the augment damage perks - I won't add perks. This causes game save breaking issues when anyone uninstalls the mod, and I don't ever want my mods to potentially break someone's game.
7. Armor has no downsides for a mage - I like the idea, and I think I know how to implement it already (using only the first perk from each school of magic)
8. Impact can stun lock bosses - I agree this is a problem. I am desperately working on trying to find a fix.
9. Master spells svck - so far, reduced casting times of destruction master spells to 1 second, and increased the damage (how much varied by spell). I'll be looking at the others individually as I examine each school of magic.
10. Some perks svck - some need work, that's for sure. I like some of your suggestions, but I think there still needs to be plenty of testing and tweaking to get them all right.
New spells - I have my own list of what's missing compared to previous elder scrolls games.