Magus definitely needs some sort of mana regeneration in the item in order for a lot of AP junglers to be even viable.
Right now, there are so few AP champions that can actually jungle right now compared to the junglers that use the other enchants, moreso Cinderhulk and Warrior, and a big reason for that is that a large majority of AP champions need to burn a lot of mana to baseline clear the jungle. An even bigger problem is that Magus doesn't help with these problems because of its lack of mana regeneration.
Magus can't really keep its current stats while also gaining a mana regeneration passive, so something needs to go to make room. I would tentatively consider completely removing the CDR for a strong mana regen passive. Maybe something like:
-80 AP
-Passive: restores mana equal to 50% of the magic damage done to monsters
Might be grossly undertuned, overtuned, or wrongly tuned (ie. too much AFK farm jungle and not enough help team), but I do like the idea of the item having just AP and the mana regen passive, as any CDR might restrict it from champions that get a lot of innate CDR (ie. Ryze, Cassiopeia, any other AP champion that gets released/reworked with innate CDR).