DISCLAIMER: I don't have the maths behind my reasoning here but I've done my research and testing, and most importantly, experience. I did my DPS test on a Magicka NIghtblade with Spell Strat, Siroria and Valkyn Skoria against a 6-Million target Dummy. Also I've written this one down in the Megathread so feel free to comment here if I make any sense.
When it comes to magicka DD races, Altmer and Dunmer feel lackluster with the changes to their passives. Compared to a Khajiit's 8% Spell Crit bonus, a 258 Spell Damage bonus is not as powerful. Ever since I've been doing 4-man and 12-man activities in ESO, Crit is always king, even after some of the nerfs received, as it scales way better with raid buffs. This would also come in tandem with the recent buff(or un-nerfing) of Shadow Mundus. Even better, Khajiit has a tiny bit of recovery no matter how negligible that is. This makes them a better Dunmer on live servers.
Also the 7% Cost Reduction on Breton is better sustain in comparison to High Elves' recently changed Spell Recharge passive(utter useless) and none to Dark Elves at all. The loss in Spell Damage bonus to Bretons can be made up by using a Berserker enchant, which grants more Spell Damage (with at least 60% uptime) than the bonuses from both Altmer and Dunmer, therefore making them more effective in DPS. On top of that, they can be tank-ier with the resistance buff received.
So what can we do to salvage Altmer and Dunmer?
1. Increase Spell Damage Bonus up to 300
2. Revert Spell Recharge passive from 4.3.2 to 4.3.0, where it will restore whichever is higher. Or better yet, keep the same passive in 4.3.2 but it should be based on Maximum percentage at a given point, instead of the Max Value, i.e. I have 70% Max Magicka and 100% Stamina at the moment, Spell Recharge will restore Magicka; if I have 60% Magicka and 50% Stamina, Spell Recharge will restore stamina. This will be a good balance but I don't think it's game breaking.
3. Since most changes are going with lore, increase Max Magicka Bonus to 2500.
1. Change Resist Flame to Destructive Ancestry, where Dunmer's would still receive Flame Damage resistance and Burn Immunity, and add an increased 50% chance to Burn enemies (or increase Burn Damage to 50%).
2. Bump Ruination to 270 Weapon and Spell Damage, or increase Dynamic to 2000 Max Magicka and Stamina.
The suggestions that I made above will someone keep most of the races' identity and would still be viable options and more appealing to everyone.