A well know author tackles a two volume biography of a major singer of the 20th Century, and produces maybe the best and most detailed biography of this singer ever.

No, no, it’s not the second volume of Gary Giddins Crosby biography (Volume One published 2001), but the second volume of the massive Sinatra biography by James Kaplan.
 
For those that have missed it, Kaplan’s  Volume One- Frank: The Voice was published in 2011 with 800 Pages, and Sinatra: The Chairman just came out last month (October 2015) at 992 Pages.

It’s been 14 years since Gibbons published Volume One and perhaps one day he will publish Volume Two, but I cannot help but feel with every year that goes by that he is losing readers/customers, so at some point will it become economically not practical to release Volume Two?
 

“…What sickens me is the running undercurrent that Giddins has lost interest in the project. If that be true than all is lost!...”
I would encourage you to go read the thread at Nitrateville:

http://www.nitrateville.com/viewtopic.php?f=16&t=15509&p=120535&hilit=+Crosby+and+Hope+
According to the thread it is not Giddins, but the publisher. It further states that Giddins was not interested/declined the e-book option.

According to the post, Bing in his contract "...exclusive rights to Crosby’s Christmas songs, including “White Christmas..." I don't think it refers to any Christmas songs, but any titles recorded for Decca. Without checking, I'm not sure but I do not believe any of Bing's post Decca Christmas recordings (for release as singles or LPs) duplicated Decca titles. I seem to remember somewhere Ken Barnes mentioning a desire at one point to include "White Christmas" on the "Seasons" album, and relating Bing's response as they would have to get approval from MCA, which he did not feel they would grant. I don't think it was just Christmas songs, as for the same album, I believe they had to get permission to redo "June in January".

As fans, we want to see materials released, but if they own the rights, a company's job is to protect their rights. Sinatra recorded many of his hits/songs for different labels, but he never signed a contract promising not to rerecord them.

"...As I said, Frank was superb in many ways - and he managed to surmount the handicap of that voice! But a disciple rarely surpasses the leader. And surely that is what Frank admitted to being?!!!..."

I have to disagree. I go back and forth between Bing and Sinatra as being my favorite singer. I agree that Sinatra was inspired by Bing, but I think what makes him unique is that he did not copy Bing, but developed his own style. Much like Bing was inspired by but did not copy Jolson.