There are several bitcoin cash specific mobile wallets (electron cash, handcash, centbee, ...), but none of them has the functionality to manage Shared Payment Groups.

Everyone that has ever had to manage a shared pool of money knows the hassle of this task.

In a kind of bitcoin cash wallet app with added functionality to manage shared resources, the publication in the blockchain of the payments would add transparency (public data but pseudo anonymous) to the management.

This new app should add specific functionality to manage the shared resources, for example it could automate the liquidations, could send invitations to join/pay our selected contacts,...

Each time a new shared account is created, a pair of keys or a whole set of HD keys should be created. That account would receive the payments of the members and its funds would be used for payments.

Only admins (members that know the private keys) could do payments, but any other member could monitor the shared account. That information could be useful to spread to non members in some cases (f.e. a new shared account is created for renting a bus to go somewhere, the provider of the service could see how many people had paid and choose the right size of the bus).

Note that it's not a trustless implementation, you should trust the admins (as today).

Using an app that facilitates those tasks would help the adoption by those group members who have not yet adopted bitcoin cash as payment. Initially only bitcoin cash advocates would act as admins but I'm sure this community would accept that challenge.

An advanced feature would allow to track fiat payments made by members to admin that would be also in the blockchain with some metadata in OP_RETURN. Also payments in fiat done by the admin should be recorded in the same way in the blockchain.