This is intended as a low cost option for people that will address some common concerns with the current pulley options. A quick change system is not in the discussion.
The point of this offering is that originally the MPX was designed with a 25% pulley arrangement in mind and certain compromises were made to achieve that pulley ratio.
1) Belt offerings that could work properly with that pulley arrangement are non-existent. You can't get a custom length belt so choices are limited to ones that are already made which means either the 400 or 390 length belts, neither of which fit properly. We have made do using spacers to raise the blower up so that the 400 belt will work, but it's a big bother and most people end up with belt slip due to the belt being too long.
2) The introduction of the abradable rotor coating and the improved MP bearing plate mean that at 25% OD the MPX makes too much boost for pump gas which means that most of you, if you upgrade to this new rotor pack, are going to have problems with excessive boost. In our dyno sessions the MPX with the new rotor pack made 2.5psi more boost than the older MPX. This is a big deal. We routinely made 20psi and 390+rwhp with our car using "only" 20% OD. The problem with that is, that even with head studs, alcohol injection, and MLS headgaskets, we lifted the heads after only one season with the car. It's just not reliable to run the car like this on pump gas even at 20% OD, nevermind 25%.
So my suggestion to Charles was to offer a stock diameter 10 rib pulley for people who have or are planning to get the new MPX rotor pack in the hopes that it would provide them a better street combination. One that makes the 400 belt fit much tighter, targets a more appropriate boost level, and reduces belt slip. It seems like a win-win to me.