Emittance dilution may increase the transverse emittance. He is simulating bunch separation and emittance dilution during transverse stacking. It seems to be working only if transverse emittance is very small. For larger tranverse emittance beams, the rms longitudinal emittance growth masked whatever gain was made. It may be a matching problem.
Investigation is currently dormant, nothing written.
However, it is generally agreed that practical rf cavities don't provide as large a kick as we would need. This may be behind Andy's skepticism. Perhaps naively, he says, he continues to be interested in approaches in which longitudinal and transverse phase space is continually intermixed. The primary conclusions are that bent solenoids are fairly complex elements which can introduce emittance growth by mismatching orbits at the beginning and end of the bend. The necessary component seemed to be coupling sections at the ends of the bends, and there were a number of ways of doing this.