It would be cool if someone could put together a sort of "Boing Bag 5" that pulled forward improvements from 3.1.4 into 3.9 as well as could be applied. Some stuff (like HDToolbox as mentioned) might have to be downgraded to the "ugly" version, but as much of 3.9 as possible could be salvaged. 3.9 was a much nicer environment than 3.1 so it would be a shame to waste what could be salvageable from it.
btw does "Long-filename" FFS introduce a new identifier/dostype to reflect the changes? If it implements long filenames using the old dostype it would cause holy hell with tools that don't understand the changes but doesn't expect them to be there by recognizing the old FFS dostype.
Or does it implement it with some semi-compatible overlay like how Joliet/VFAT implements long filenames in Windows? (ISO-9660/FAT 8.3 MS/DOS-compatible filenames with extra metadata to contain the long names).