Remember that the Pearl 2 has a fully regulated supply and lots of capacitance onboard, the outboard PSU is made to get the transformer physically away from the RIAA, and to keep the noisiest part of the PSU (switching and the ripple caps) also away from the sensitive circuits.
If you are going to do a shunt reg (which would be nice, no doubt, and I'm fairly sure someone has done one with the Salas Low Voltage shunt reg, with good results) you will need to remove the onboard series regs, not just make the outboard PSU fancier.