If I were to so something like this (which does allow for more stuff for casters to find, and new ways to customize casters,) I would give each type a damage die and some other benefit, and have the cantrips use the implement's damage die.
Ie wands do 1d4 damage with damage cantrips, but have a property like 'light' that makes using them twice in a round easier.
Rods would have a more solid d6. Staves would have a d8 but require both hands somehow (though I'm not sure the downside is strong enough to make this a real differnce. You'd need some stronger upside to a free hand.)
Then cantrips would tack onto that: firebolt does one die type better damage, ray of frost does implement damage plus the slow effect, EB scales with extra attacks, poison spray does double dice, etc.
That's still a pretty big change to a lot of game elements for a small difference in actual play, though.
Ie wands do 1d4 damage with damage cantrips, but have a property like 'light' that makes using them twice in a round easier.
Rods would have a more solid d6. Staves would have a d8 but require both hands somehow (though I'm not sure the downside is strong enough to make this a real differnce. You'd need some stronger upside to a free hand.)
Then cantrips would tack onto that: firebolt does one die type better damage, ray of frost does implement damage plus the slow effect, EB scales with extra attacks, poison spray does double dice, etc.
That's still a pretty big change to a lot of game elements for a small difference in actual play, though.