It would be really nice to add to HxD 'Structure Viewer' feature to view PE header, BMP header ar any custom structure. Something like 'Structure Viewer' in ICY Hexplorer http://hexplorer.sourceforge.net/
... and add basic display of byte/word/dword/... values on cursor position
... and split edit window on two parts like in MS Word/Excel
... also coloured file comparison would be more helpfull
... also 'Pixel Viewer' like in ICY Hexplorer , this could be easy programming task
... and Disassembler, this could be much more difficult programming task but free source code on the internet should help a bit