they're different sport and it wouldnt work however MMA and San Shou rules kickboxing might for those unfamiliar It's kickboxing with throws and takedowns was best to watch when Cung Le was doing it http://www.youtube.com/watch?v=3r55mxK2xKc
You would sell out if you mixed top fighters from both sports against each other. THe MMA guys would tune in for satisfaction hoping that their guys would kick the **** out of the boxers and the boxing fans would tune in to see the boxing fans kick the **** out of the MMA guys. WIth so much bad blood between the fans of these 2 sports it would really sell.
It happens with Thaiboxing and mma in Holland, and K-1 obviously. It is interesting to see both, but not really great. The ring is either too small for mma of too big for kickboxing/ boxing more importantly, mma belongs in a cage! Nearly ever argument against the cage is just wrong or just contrarian for it's own sake because the person hates the ufc.