What you will likely have is some pretty extreme stratification, where
the elevated returns are, besides reduced heating efficiency.

At least if he put the discharges near the ceiling with the returns
below, you'd have a manageable loop, just be overheating air at
ceiling.

What I've found to work very well, for heating and cooling is plastic
flow-diverters that magnetically attach to registers. E.g. instead of
cooled air flowing across floor to return, diverter makes it ascend for
a bit and mix with room air well above ankle-height. Much cheaper, and
more effective, IMHO than raising return.

OTHO, if return and discharge were reversible summer-to-winter, you'd
be in business.

HTH,
J