This is a great idea and almost exactly what I was looking for since I manually update my versions on Release (to testing). The format I use is taken from my days as a DNS administrator and the way I versioned DNS changes.
I use None.None.YYMM.DDBB where BB is the daily build number. This is a simple way to ensure a value that will always increase and is easily translated to a date of release.
Unfortunately as it stands your add-in doesn't support that.
So what I would suggest is you allow a string format to be supplied that would be used against DateTime.Now or DateTime.UtcNow. That wouldn't allow me to do exactly as I do now but it would allow something closer with "yyMM" and "ddHH"
and allow all users of your add-in a greater degree of flexibility in formatting their version numbers.
A handy reference for string formatting is http://blog.stevex.net/string-formatting-in-csharp/