I think the first direct benefit of (private) UDAs on Zcash would be more transactions in the shielded pool. Since Zcashs core value proposition is privacy then the stronger the privacy Zcash provides, the more valuable Zcash is to all users.
The second part, which is what I think you are getting at, is how do we make sure “ZEC the coin” itself is part of the value proposition of Zcashs UDAs?
A couple ideas:
What about mint/spend/transaction fees that must be paid in Zcash? Similar to how ETH uses gas fees?
I’m not an engineer, but is there a way to ensure users “stake” ZEC in a liquidity pool (privately) to start/use those UDAs?