It would also be perfect if we could allocate a particular bank account (ie credit card account) to a particular user so that they can do the reconciliation without admin having to push paperwork requests through.

Xero doesn't allow for this level of granularity in user permissions, and we always have clients wanting visibility of their credit card transactions + outstanding documents to be uploaded.

Essentially, I would imagine it would be a Bank Transactions screen like the one in the screenshot attached (but limited to the assigned/linked accounts for the user).

This functionality could be expanded further by showing a running total of the balance for the account, and if it's a credit card the ability to set a credit card limit to show available funds remaining.