Perhaps there could be a rigid structure made , but a weight penalty in doing so..
always a balancing act.. perhaps as I don't pull on the bars , while I ride
There seems to not be a flex concern..
different from Both, seen on their website,
BTO Bike Friday's Folding stem for their 20" wheel bikes.. is mostly aluminum ,
once QR lever is opened It has a spring catch pin for safety,
a sliding up of a sleeved section,
then the fold over can take place.. quite a clever bit
they dont make it , it comes from a Taiwan company
1" quill, fixes inside a 1.125" threaded fork .
on top there is a height adjustment, then a Threadless stem clamps on that tube.
BF has thru threaded lock nuts on their headsets,
then an extra piece above the HS
clamps on & adds more strength..
Home machine shop would be a handy thing .. in the best of all possible worlds..