Im only talking about the last suggestion with a normal double sided track hub plus loose disc adapter.
The disc adapter is probably 7mm thick so the disc line is probably going to be 44 mm instead of 41.5mm.
Could be a problem with rearstays (or maybe not :) ).
and as @M_V says if you want to change things regularly.
also I found spoke clearance can be a problem (caliber hits spokes on some combination) so maybe you want a wide disc line (44-45mm)
Maybe buy a bunch of all the various spacers for every combination!
look here I have done related stuff: Dolan plus disc brake