Thanks for your suggestion.
Internally, we have been looking to implement PayPal Billing Agreements for a little while, however, PayPal have advised that they are working on a new product to be launched soon that will supersede the currently available billing agreements product, and based on the recommendation from PayPal our intention is to integrate with this new PayPal product once its available.
Whilst we presently do not have a precise ETA on this, we currently have indications from PayPal it will be released early next year.