Be a little windy inside in the winter, but you could size one system
to the cooling load, look at its winter heat output then size the
second one to make up the difference .

You would eliminate heat strips for maintaining comfort but you would
still need heat strips to recover from the setback. If you want to live
with the lowered temperature while the system is trying to recover, why
set it back in the first place? Wear wool socks, bunny slippers, long
underwear and a sweater all winter.

Making the second heat pump large enough so that the combined heat
output was triple the design heat load, would eliminate the heat strips
on the set back but you have the problem of the second system short
cycling all the time except when revovering from the setback.