Dual Ignition Systems
For a homebuilt or ultralight, yes.  There are high voltage diodes that take a high tension lead from 2 separate sources with a single output, made for racing, that allow you to run a single plug from either of two sources, whatever they are.  They are popular on Corvair aircraft engine conversions.   You can run a mag and battery system together, or two battery systems, or whatever, with a one-or-the-other ignition switch.