I came up with the idea of having shared item bank for all 3 heroes. The idea of it is that you would be able to put looted items in a different inventory than your heroes inventory who you are using at that moment. For example my monk has 3 runes that my warrior needs, I could just put those runes into "bank" amd switch to my warrior and take those runes from "bank". This system is in the other games and it works like a charm.
To compensate possible money losses develorpers could make it very small, 5 slots for example and add very expensive expansion, for example 200 gems/ 1 million coins. Yes you could choose if you want to expand it with real money or with coins.
Hopefully you fellow players like this idea