They could support a more sophisticated charging system in addition to supporting power delivery. Finer-grained, dynamic control of power delivery might let them be more aggressive with charging speed based on device usage, battery capacity, and heat.In regards to charging speeds though, I believe the EU law requires that any device supporting fast charging must support USB-C Power Delivery. So Apple can't apply MFi restrictions to fast charging.
As a baseline, I would expect them to support 20W charging and USB 2.0 speed, because thats what the non-pro iPad supports today with the A14.