Although the 1571 is capable of reading and writing both sides of a disk, accesses to the second side using the second head will be performed with the drive spinning in opposite direction from how it would be read if inserted upside-down and accessed with the first head (only head on the 1541). Conceptually, however, it would seem like it should be possible to write a disk which could be read in either direction, either by:
If one only needed to use about half the capacity of the second side, one could format the disk side with a mixture of forward-written and reverse-written sector headers. Track 18, for examine, which would normally contain 17 sectors, could have eight reverse-written headers for sectors 0-7, followed by eight forward-written headers for sectors 0-7. If the BAM for the "read as flippy" direction marked as "used" all of the sectors that didn't exist in that direction, inserting the disk as a flippy would simply make it appear as a normal disk that appeared full despite having less than 85K of stuff on it. Presumably, to make the other side compatible with 1541 drives, it would be formatted as a normal 170K disk, so any data on the reverse would have to be accessed using track/sector accesses.
If one needed to use more of the capacity, one could write much of the data using a custom format that would precede each sector with a forward-written header and immediately follow it with a reverse-written one. Reading a reverse-written sector would require different decoding logic from reading a forward-written one, but I don't think the drive electronics should care about whether the data is being read forward or backward.
Would such a thing have been possible? Has anyone ever done it, either back in the day or in the "retro-computing era"?