I agree, it is way too early for a fill-in artist. It'd be O.K. after the 12 issue story-arc.
The only way I could imagine a different art style working in this issue is if the underlined below from the solicitation comes into play - it has to be executed really well to work though.
KING CONAN REIGNS AS “THE LIFE AND DEATH OF CONAN” CONTINUES!
• A hard-fought life has rewarded CONAN with the crown of Aquilonia… • But even a monarch must face the cold embrace of death! • The legendary adventure continues as the CRIMSON WITCH makes good on her threat to King Conan!