1) Obvious -- having edits able to be saved for proper binary editing. I can see that this might be rather difficult though, unless you can control how the user applies edits (in which case, things could get very slow!)
This is not impossible, but will be a little tricky. I will probably need to restrict some things and give warnings to malformed data. I am saving this for the very very end. The viewer will be released without edit capability and then I will revisit and see how I may go about adding this.
2) A list of file extensions; if a file with an extension in the list is opened, the real file is closed and the hex_viewer representation is automatically opened.
I have experimented with this, but ST2 doesn't always fire the event for opening a file correctly...or at least as expected. It has caused me some issues to do this. I may revisit this again when I get the essentials in.
3) An ability to add extension-specific representation. For example, if the extension is BMP, rather than just displaying a simple set of words and their ascii, display the BMP structure header and display the body in standard hex format. Perhaps this is well beyond the intention of Hex Viewer.
Can you provide more in depth explanation to BMP structure headers? Is there an hex editor that does this sort of thing that I could view as an example? I would like to take a look into this before I give a yes or a no.
Is there a way to bind a key to the "Hex Viewer: Toggle Hex View" command?
Yes, you just use the standard key binding methodology. I will post an example in a bit.