This is already possible.
1. Run a Transaction List by Date report (Reports > Accountant > Transaction List by Date)
2. Click Modify Report... > Display and select the Type, Date and Num columns
3. Click Modify Report... > Filters. Choose the TransactionType filter and add Tax Invoice ** You can add multiple transaction types such as Sales Receipts if you use both in your business.
4. Click OK
5. Select All dates, sort by Num (descending). The last used invoice number will now appear at the top of the list.
6. Memorise the report to use again later