Well, it's the removal of the amp envelope that's applied to the tail, or at least the application of an all-on one, so in theory it shouldn't require a new engine or anything near that - just the addition of the envelope to the code and a parameter choice to disable the standard fade... IMHO.
If an amp envelope isn't employed and instead the KPA subtracts a level value from each repeat, the temporary suspension of this action will be all that's necessary, and again, along with the addition of a parameter allowing for fades to be bypassed.
As for the number of repeats, obviously that'd be determined by the algorithm used; we'd have to choose from the various number of taps available.