I don't dispute your knowledge of the INP related code in Mame32, but are you sure about the fact that Mame32 has *never* cared about the data stored in the .hi files?(posted 9798 days ago)My reasoning behind this is that in versions of Mame32 released before version 34b2, games that stored data in the .hi file (mspacman for instance) would pass that data along when an inp file was played back (i.e., the high score would not necessarily be -0-). Specifically in mspacman, this has a definite effect on the results of inp file playback, as the game uses a different set of seed values for the semi-random control of the ghosts.
I do agree with you, however, that the latest versions of Mame32 are incompatible due to changes in the inp file system (but this has been happening since the earliest support of inp files in Mame - inp's have always been very inconsistent between different versions of Mame).