Well, there are many questions about z-values. Extracting them from transactions, and signed messages, can be tedious.
To be clear the z-values aren't part of the transaction so they are not stored in the blockchain to be "extracted". They have to be computed, then the explorer has to store this additional data on top of what they are storing (that is tens of gigabytes of additional data).
I honestly don't see the utility for such a explorer though.
Talking about different explorers, someone was recently Talking about a OP_RETURN explorer, which would allow users to search for particular messages written in the blockchain. This could be a more interesting idea imo