Both Smiths to start in the 6 Nations?

We saw it against Japan in the autumn, Fin at 10 and Marcus at 15, now with Furbank most likely out of some (if not all) of the 6 nations with a broken arm could we see them together? I know Steward is the natural replacement but as we saw against Bath, Fin is brilliant. On the other hand, Marcus is 100% undroppable right now for England. Could the 2 of them together at 10 and 15 work?