Hard to poll such a fundamental disruption but IMO split Con party plus united Lab party most likely to deliver large Lab majority unless the two Con parties are willing to do deals on who stands where
In addition,majority of voters who don't follow politics closely wld find split v confusing. Interesting Q would be what signals they follow: signals about which party is "real" Cons? Or signals about which party is "real" Brexit party (which might be UKIP rather than either Con)
*If* the split resulted in large chunk of Con Leave voters backing a "hard Brexit" Cons, and soft Leave/Remain Cons backing a "soft Brexit" Cons, then even with co-ordination of seats the most likely consequence would be loss of a lot of seats. 3/4
Many Con majorities depend on mix of hard leavers, soft leavers and remainers. Pull out one leg of the stool, and the seat is gone. So my advice would be to be careful what you wish for @andrew_lilico !
