I assume it is a big rewrite as well - but the question is "how big"?
As to the other questions:
1) XML may make understanding the format a bit simpler because of the "wordiness" of XML data, which will be easier than dealing with a binary format. Once it's understood, it makes it easier to create tools which do things like supernudelist (i.e. create pages of buttons for CD changers). XML was designed for this kind of usage, after all.
2) I think it is a given that current Pronto tools are useless (except to the degree that they can generate a CCF which can be imported into ProntoEdit NG). My point is that if we are switching to a new format, an XML-based format is a good one to switch to.
3) I'm not an IR expert, but I did a quick trial. I compared the power code for my Panasonic DVD player in ProntoEdit 4 and in ProntoEdit NG (after importing from the PE4 CCF, of course), and the codes were similar but not quite identical.
