An initial feature request is for a simple buffer byte-swap, edit / tool option. This would be very useful for the Retro community, where we often need to do a file byte-swap where ROM images (for eg. big-endian 68000 based systems) have the bytes in the wrong sequence, presumably due to the ROM image file being created on a PC? (Intel little-endian).
Whatever the cause for the incorrect byte sequence ROM image files, it is often necessary to swap bytes in a file before writing out to an EPROM (for example).
Having this capability in HxD would make it a all-in-one solution, along with it's existing Hex editing and File Split / Concatenate tools.