Almost certainly shear failure first, without rebar there is nothing to take the horizontal tension. You could potentially make this work but I'd be extremely skeptical of it's long-term success. I use plain concrete shiplap joints all the time in precast but for non-critical connections like joints between panels and such.
Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)