When I made a decision to switch to Legere reeds a couple of years ago I reversed the usual paradign (as you described) by looking for mouthpiece facings and ligatures that give me the best possible quality of sound from Legere. This is not exactly what you describe in having 2 mouthpieces with facings that can cover softer or harder reeds in a box. However, what I did is along the lines of matching mouthpieces to a reed rather than the usual way of matching reeds to a mouthpiece.
With the approach I've taken I'm able to get a truly beautiful sound with Legere reeds using Walter Grabner's clarinet and bass clarinet mouthpieces. Happily, I found that Legere reeds also sound really good on the Morgan 6C tenor mouthpiece that Ralph custom made for me a few years ago. Recently, I sent my backup 6C to Brian Powell along with a new Legere reed and asked Brian to adjust the mouthpiece facing so it works better with Legere reeds. Brian made some changes to the facing curve and took in the side rails. The mouthpiece now plays beautifully! Truly, a night and day difference.
I've found it to be really funny in how, on some discussion threads on the Forum, I've described the quality of sound I get with Legere reeds on the mouthpieces I've come to use and it appears that some folks don't believe me. But, it's true! Legere reeds sound terrible on some facings. If one has only experienced Legere in that way then I can understand how they might have a problem in believing someone who talks about the reeds in glowing terms. But, as I've discovered, it comes down to having a good match between the reed profile and the mouthpiece facing.