What you get here will be perceived as stereo, but it will be fake and suffer from an extreme phasing-problem in the right channel (providing it's the right channel you reverse, it normally is in M/S).
What you have here is actually, except the phase-reversal part, something I've used on several occasions to make broken, phased-out, FUBAR sound effects. In mono.
The reason M/S actually works so well is that the Figure Of Eight-mikes are dually polarized, ie the membrane is positive on the front side and negative on the rear side. Then when you split up the Mid into two discrete channels with phase-reversal on the right one, left channel will enhance the positive signal in the mid-mic and attenuate the negative, and the right channel will do exactly the same thing, though opposite.
When you do not have an Eight to record the Mid's with, there will be no difference in phase between left and right, and after matrixing you will get a signal with the left signal having a slightly higher directivity than the Cardio though lower than the Hyper and about 1.5dB louder (depending on how well you matched 'em), the right channel will sound thing, phased-out and without a core.
You can never replace the Eight in an M/S-recording, but you can actually do pretty much what you want with the Mid! I don't have any Figure Of Eight's right now since one of my Oktava's went belly up, but when I did I experimented a lot with everything between Omni's to Lobar's, and even another Eight with very nice results! Unlike in for example X/Y (personal favorite) or A-B and such, it doesn't really matter if the mics are matched or not, I've tried out everything from Oktava, Sennheiser, DPA, AKG, Shure, and several other high quality mics (I like to work with micings so I put my paws on everything I can get!), and even some rather bad one's from both ADK, Röde and Pulse (don't ask...) to mention a few (as I said, EVERYTHING I can get :-)) with different sounding but often greatly working results depending on what I want right then :-)