It doesn't make anything with the purging if u cut out the plate, because with a common chamber rig when u want to purge, the air from the hose port goes nearly directly to the purge valve. The fact why traditional rigs are better is, that because of the tub which come from the hose port, the air is forced down to the bottom of the base and thats why u can purge with a rig like this better.
But i would be intrested in it too, what happens if u cut out the plate from a common chamber rig, or u simply just add some more holes to it? The purging won't be better, i know, but what about the smoke? But as far as my studies learn it to me as long as the diameters of the holes on the covering plate of the common chamber are the same or more than the diameter of the downstem it won't do anything special if u make more holes on it
I hope u got what i want to say