From a brief review of the proposal it appears the BATFEIEIO is aiming at reclassifying any mechanical device which, when attached, activated, or otherwise initiated by a single movement of the operator's finger, creates a continuous fire condition from an otherwise semi-automatic weapon. From what I'm reading the biggest change is the proposed revision of what is considered an initiating action - from "pull of the trigger" to "movement of the shooter's finger". Existing determinations hinged on that technicality so the minor wording change would mean a wholesale shift in analytical context. They specifically mention bump stocks but the overall language is more inclusive, essentially covering any device which can create the condition.
In short, what I'm seeing is a proposal to re-classify any device that can be attached to a weapon for the express purpose of allowing a single finger movement to initiate a constant-fire condition. This would apply even if the weapon the device is attached to remains intact and unmodified.
Brad