Jack,
I have previously tried your suggested technique with mediocre results, the fit has to be precise. I am adding Wenge "breadboard" ends to two highly figured live edge slabs in order to extend the length of the table. The material is 2 3/8" thick and the joints are primarily endgrain to endgrain, actually, there are curves to make it all the more fun. At the outboard edges I need a really strong (deep) floating tenon to support the cantilever. The Wenge tenons will be pinned in order to pull the pieces together while allowing lateral movement from expansion/contraction. The 14mm domino mortise would be close to an ideal solution.
Unfortunately I can't figure out how to attach a photo for clairification.