For Revolving credit account (could be coupled with billing cycles or not), ability to calculate instalment due as % of outstanding principal at the moment of last billing cycle end/disbursement (each new end of billing cycle that had some new purchases or at each disbursement when there is no billing cycle). In case the billing cycle has no new purchases, principal due is the same as previous month unless the outstanding principal is less or zero (not recalculated). Interest, fees and penalties are added on top of the principal in each instalment according to configured methodology.
Prepayment of the upcoming instalment should mark it paid in case of total or principal prepayment based on what is configured.
This calculation method would enable end clients to have equal repayments following the last disbursement and have a finite schedule.