How can we improve WHMCS?

I would like to be able to set an upper value for a payment gateway so that orders/invoices above that amount removed that particular payment option from being used.

ie I have 3 payment gateways, PayPal, Stripe and Bank Transfer.
I would set an upper threshold of £1000 on both PayPal and Stripe (although it could be different amounts) which would mean orders/invoices over this value could only be paid by bank transfer.

This isnt specific to any particular payment gateway so shouldnt be the payment gateways themselves getting changed