So, if I'm reading Jeff's idea right,
MEC would allow someone to cast round 1, cast round 2, then consider whether to burn their free action to cast again (and stay out of combat) or not, if not, cast round 3 (and likely use MEC here).
I really like the MEC as is. I think we could change it to 1/round, as an instantaneous action, take 10 eldritch damage to add 15 (non-eldritch damage type) to your next spell cast. This would be more than current 1st level spells with a successful spell check, less than 2nd and 3rd, but would not force the Wizard to guess when to use a free action.
It would also free the MEC from being tied to skill checks, opening up that design space for Relic and Legendary tokens.
It would continue to allow wizards access to other free actions (Cabal set, Ring of Spell Storing, etc).
Am I missing something incredibly obvious?
Also, I really don't love the idea of breaking wands to deal a ton of damage, with a 25% chance of needing to be resurrected, unless you have over 100 HP.