I just checked with Bill, and he said he enjoyed monos equally to the stereo when he heard the Sumile stereo on Vyger, RS on Vyger, and Madake on Vyger.
So this is also quite a function of the Vyger LT. Could a dedicated mono sound better, maybe, but imo if you could flip stereo and mono and they sound equal on the vyger, adding a mono cart to beat the stereo cart on monos, is like trying another stereo cart to beat existing stereo cart on stereo pressings. You might get better, or you might not, depending on how good the mono cart is.
There are also other variables like the entire system, because on some systems monos sound good with stereo carts while on some they sound broken. This could be a function of the phono, the speaker placements, etc.