Alright, not too many more posts since I left for my walk. There are a few good ideas out there and a lot to think about. I'm just going to throw my thoughts out there (as I tend to do at times).
There is no other legendary I've acquired that caused me to hesitate as to whether or not it was better than what i was giving up. Why does it have to be this one? First, too much wizard ability has been tied up in the neck slot either directly through MoMM or indirectly through the Charm Necklace. People giving up those items shouldn't feel like they're losing almost as much as they gain.
Adding MEC to the legendary recovers 1/3 of what we lose. Go the rest of the way. Add Spell Swapping ability to the token and if you want to improve it, allow swapping for same level spell or lower (last part optional). Then make it a Medallion of the Cabal. Yes, make it a fourth Cabal item, but still only require that 3 of the 4 be equipped to acheive the FA spell cast once per room. Then add spell damage to the equation; something like +3 at the relic level and +5 at the legendary level to help compensate for loss of MoMM. This allows various wizard paths to converge at the legendary level and each have access to all the "tricks of the trade". You will probably need to reprint the other Cabal items no later than next year.
Another benefit is that newer players can focus on the transmute path and not worry about waiting until all the cool wizard URs are reprinted sometime over the next 10 years. Yes, I'm sure Bards, Clerics and Druids might be upset they didn't get a 4th Cabal item, but they don't lose anything. In fact, if more wizards start equipping Cabal items they will indirectly benefit. It will also breathe new life into that set.
In the end, I no longer need to equip MEC, CoSS or Charm of the Cabal (optional), thus not making me feel like I'm losing anything in the upgrade. I will still gain some benefits worth the cost of the transmutes. I also gain more flexibility with the Cabal set. Maybe I'll find a way to equip the Charm and replace the Gloves with Blessed Tempest and gain a little more spell damage.
Anyway, this is something I'd be happy to add to my build at the cost of a relic and legendary.