It definitely is frustrating not to know what happened. I do applaud them for shaking things up a bit- most people would simply write [four?] years in the future as though nothing had changed. They clearly have some idea about what went on in those missing years, as there's references to it all the time.
It seems that in the recent interviews they've teased the idea of revisiting that time period. I'm not sure if this has any bearings as I'm relatively 'new' to the fandom, but DS9 seems to have grown in popularity thanks to streaming sites like netflix.
This book was listed as one of the top selling trek books on amazon for a little bit, although I'm not sure if that's simply a weekly list or an all time list. Hopefully that indicates its done well.